[Flang] Move markdown files(.MD) from documentation/ to docs/

[sameeranjoshi]

Summary

Other LLVM sub-projects use docs/ folder for documentation files.
Follow LLVM project policy.

Modify documentation/ references in sources to docs/.
This patch doesn't modify to reStructuredText(.rst) file format.

[sameeranjoshi]

The docs still render on github.
See a more friendly version below.
https://github.com/Sameeranjoshi/llvm-project/tree/sam-move-md-to-docs/flang/docs

[DavidTruby]

LGTM

[sscalpone]

I think you missed one.

[sameeranjoshi]

In D85884#2218264, @sscalpone wrote:

I think you missed one.

I didn't find what did I miss.
@sscalpone Can you please point what is missing?

[sameeranjoshi]

Fix review comments.

flang/README.md

 # Flang
 
 Flang is a ground-up implementation of a Fortran front end written in modern
 C++. It started off as the f18 project (https://github.com/flang-compiler/f18)
 with an aim to replace the previous flang project
 (https://github.com/flang-compiler/flang) and address its various deficiencies.
 F18 was subsequently accepted into the LLVM project and rechristened as Flang.
 
 ## Getting Started
 
-Read more about flang in the [documentation directory](documentation).
-Start with the [compiler overview](documentation/Overview.md).
+Read more about flang in the [docs directory](docs).
+Start with the [compiler overview](docs/Overview.md).
 
 To better understand Fortran as a language
 and the specific grammar accepted by flang,
-read [Fortran For C Programmers](documentation/FortranForCProgrammers.md)
+read [Fortran For C Programmers](docs/FortranForCProgrammers.md)
 and
-flang's specifications of the [Fortran grammar](documentation/f2018-grammar.txt)
+flang's specifications of the [Fortran grammar](docs/f2018-grammar.txt)
 and
-the [OpenMP grammar](documentation/OpenMP-4.5-grammar.txt).
+the [OpenMP grammar](docs/OpenMP-4.5-grammar.txt).
 
 Treatment of language extensions is covered
-in [this document](documentation/Extensions.md).
+in [this document](docs/Extensions.md).
 
 To understand the compilers handling of intrinsics,
-see the [discussion of intrinsics](documentation/Intrinsics.md).
+see the [discussion of intrinsics](docs/Intrinsics.md).
 
 To understand how a flang program communicates with libraries at runtime,
-see the discussion of [runtime descriptors](documentation/RuntimeDescriptor.md).
+see the discussion of [runtime descriptors](docs/RuntimeDescriptor.md).
 
 If you're interested in contributing to the compiler,
-read the [style guide](documentation/C++style.md)
+read the [style guide](docs/C++style.md)
 and
-also review [how flang uses modern C++ features](documentation/C++17.md).
+also review [how flang uses modern C++ features](docs/C++17.md).
 
 ## Supported C++ compilers
 
 Flang is written in C++17.
 
 The code has been compiled and tested with
 GCC versions from 7.2.0 to 9.3.0.
 

flang/docs/ArrayComposition.md

-<!--===- documentation/ArrayComposition.md 
+<!--===- docs/ArrayComposition.md 
   
    Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
    See https://llvm.org/LICENSE.txt for license information.
    SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
   
 -->
 
 This note attempts to describe the motivation for and design of an

flang/docs/C++17.md

-<!--===- documentation/C++17.md 
+<!--===- docs/C++17.md 
   
    Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
    See https://llvm.org/LICENSE.txt for license information.
    SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
   
 -->
 
 ## C++14/17 features used in f18

flang/docs/C++style.md

-<!--===- documentation/C++style.md 
+<!--===- docs/C++style.md 
   
    Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
    See https://llvm.org/LICENSE.txt for license information.
    SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
   
 -->
 
 ## In brief:

flang/docs/Calls.md

-<!--===- documentation/Calls.md
+<!--===- docs/Calls.md
 
    Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
    See https://llvm.org/LICENSE.txt for license information.
    SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 -->
 
 ## Procedure reference implementation protocol

flang/docs/Character.md

-<!--===- documentation/Character.md
+<!--===- docs/Character.md
 
    Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
    See https://llvm.org/LICENSE.txt for license information.
    SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 -->
 
 ## Implementation of `CHARACTER` types in f18

flang/docs/ControlFlowGraph.md

-<!--===- documentation/ControlFlowGraph.md 
+<!--===- docs/ControlFlowGraph.md 
   
    Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
    See https://llvm.org/LICENSE.txt for license information.
    SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
   
 -->
 
 ## Concept

flang/docs/Directives.md

-<!--===- documentation/Directives.md 
+<!--===- docs/Directives.md 
   
    Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
    See https://llvm.org/LICENSE.txt for license information.
    SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
   
 -->
 
 Compiler directives supported by F18
 ====================================
 
 * `!dir$ fixed` and `!dir$ free` select Fortran source forms.  Their effect
   persists to the end of the current source file.
 * `!dir$ ignore_tkr (tkr) var-list` omits checks on type, kind, and/or rank.

flang/docs/Extensions.md

-<!--===- documentation/Extensions.md 
+<!--===- docs/Extensions.md 
   
    Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
    See https://llvm.org/LICENSE.txt for license information.
    SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
   
 -->
 
 As a general principle, this compiler will accept by default and

flang/docs/FortranForCProgrammers.md

-<!--===- documentation/FortranForCProgrammers.md
+<!--===- docs/FortranForCProgrammers.md
 
    Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
    See https://llvm.org/LICENSE.txt for license information.
    SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 -->
 
 Fortran For C Programmers

flang/docs/FortranIR.md

-<!--===- documentation/FortranIR.md 
+<!--===- docs/FortranIR.md 
   
    Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
    See https://llvm.org/LICENSE.txt for license information.
    SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
   
 -->
 
 # Design: Fortran IR

flang/docs/IORuntimeInternals.md

-<!--===- documentation/IORuntimeInternals.md
+<!--===- docs/IORuntimeInternals.md
 
    Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
    See https://llvm.org/LICENSE.txt for license information.
    SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 -->
 
 Fortran I/O Runtime Library Internal Design

flang/docs/ImplementingASemanticCheck.md

-<!--===- documentation/ImplementingASemanticCheck.md 
+<!--===- docs/ImplementingASemanticCheck.md 
   
    Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
    See https://llvm.org/LICENSE.txt for license information.
    SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
   
 -->
 # Introduction
 I recently added a semantic check to the f18 compiler front end.  This document

flang/docs/Intrinsics.md

-<!--===- documentation/Intrinsics.md 
+<!--===- docs/Intrinsics.md 
   
    Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
    See https://llvm.org/LICENSE.txt for license information.
    SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
   
 -->
 
 # A categorization of standard (2018) and extended Fortran intrinsic procedures

flang/docs/LabelResolution.md

-<!--===- documentation/LabelResolution.md 
+<!--===- docs/LabelResolution.md 
   
    Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
    See https://llvm.org/LICENSE.txt for license information.
    SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
   
 -->
 
 # Semantics: Resolving Labels and Construct Names

flang/docs/ModFiles.md

-<!--===- documentation/ModFiles.md 
+<!--===- docs/ModFiles.md 
   
    Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
    See https://llvm.org/LICENSE.txt for license information.
    SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
   
 -->
 
 # Module Files

flang/docs/OpenMP-4.5-grammar.txt

-#===-- documentation/OpenMP-4.5-grammar.txt --------------------------------===#
+#===-- docs/OpenMP-4.5-grammar.txt --------------------------------===#
 #
 # Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 # See https://llvm.org/LICENSE.txt for license information.
 # SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 #
 #===------------------------------------------------------------------------===#
 
 # OpenMP 4.5 Specifications

flang/docs/OpenMP-semantics.md

-<!--===- documentation/OpenMP-semantics.md 
+<!--===- docs/OpenMP-semantics.md 
   
    Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
    See https://llvm.org/LICENSE.txt for license information.
    SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
   
 -->
 
 # OpenMP Semantic Analysis

flang/docs/OptionComparison.md

-<!--===- documentation/OptionComparison.md 
+<!--===- docs/OptionComparison.md 
   
    Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
    See https://llvm.org/LICENSE.txt for license information.
    SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
   
 -->
 
 # Compiler options

flang/docs/Overview.md

-<!--===- documentation/Overview.md 
+<!--===- docs/Overview.md 
   
    Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
    See https://llvm.org/LICENSE.txt for license information.
    SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
   
 -->
 
 # Overview of Compiler Phases

flang/docs/ParserCombinators.md

-<!--===- documentation/ParserCombinators.md 
+<!--===- docs/ParserCombinators.md 
   
    Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
    See https://llvm.org/LICENSE.txt for license information.
    SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
   
 -->
 
 ## Concept

flang/docs/Parsing.md

-<!--===- documentation/Parsing.md 
+<!--===- docs/Parsing.md 
   
    Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
    See https://llvm.org/LICENSE.txt for license information.
    SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
   
 -->
 
 The F18 Parser

flang/docs/Preprocessing.md

-<!--===- documentation/Preprocessing.md 
+<!--===- docs/Preprocessing.md 
   
    Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
    See https://llvm.org/LICENSE.txt for license information.
    SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
   
 -->
 
 Fortran Preprocessing

flang/docs/PullRequestChecklist.md

-<!--===- documentation/PullRequestChecklist.md 
+<!--===- docs/PullRequestChecklist.md 
 
    Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
    See https://llvm.org/LICENSE.txt for license information.
    SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 -->
 
 # Pull request checklist

flang/docs/RuntimeDescriptor.md

-<!--===- documentation/RuntimeDescriptor.md 
+<!--===- docs/RuntimeDescriptor.md 
   
    Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
    See https://llvm.org/LICENSE.txt for license information.
    SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
   
 -->
 
 ## Concept

flang/docs/Semantics.md

-<!--===- documentation/Semantics.md 
+<!--===- docs/Semantics.md 
   
    Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
    See https://llvm.org/LICENSE.txt for license information.
    SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
   
 -->
 
 # Semantic Analysis

flang/docs/f2018-grammar.txt

-#===-- documentation/f2018-grammar.txt -------------------------------------===#
+#===-- docs/f2018-grammar.txt -------------------------------------===#
 #
 # Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 # See https://llvm.org/LICENSE.txt for license information.
 # SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 #
 #===------------------------------------------------------------------------===#
 
 R0001 digit -> 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9

flang/docs/flang-c-style.el

-;;===-- documentation/flang-c-style.el ------------------------------------===;;
+;;===-- docs/flang-c-style.el ------------------------------------===;;
 ;;
 ;; Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 ;; See https://llvm.org/LICENSE.txt for license information.
 ;; SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 ;;
 ;;===----------------------------------------------------------------------===;;
 
 ;; Define a cc-mode style for editing C++ codes in Flang.

flang/lib/Evaluate/intrinsics.cpp

 using namespace Fortran::parser::literals;
 
 namespace Fortran::evaluate {
 
 class FoldingContext;
 
 // This file defines the supported intrinsic procedures and implements
 // their recognition and validation.  It is largely table-driven.  See
-// documentation/intrinsics.md and section 16 of the Fortran 2018 standard
+// docs/intrinsics.md and section 16 of the Fortran 2018 standard
 // for full details on each of the intrinsics.  Be advised, they have
 // complicated details, and the design of these tables has to accommodate
 // that complexity.
 
 // Dummy arguments to generic intrinsic procedures are each specified by
 // their keyword name (rarely used, but always defined), allowable type
 // categories, a kind pattern, a rank pattern, and information about
 // optionality and defaults.  The kind and rank patterns are represented