[flang] Convert release notes to markdown

[richard.barton.arm]

Summary

Switch ReleaseNotes from .rst to .md to match the other docs.

At the same time, fix the version number for master.

[sscalpone]

flang/docs/ReleaseNotes.md

34

Does this line need an edit for llvm 12?

[sameeranjoshi]

Thanks for revisiting this.

[richard.barton.arm]

flang/docs/ReleaseNotes.md

34

I don't think so. Flang is new for the LLVM 11 release and will not be for the LLVM 12 release. I'm just applying the changes to master first before backporting to the release branch.

I suspect that we will end up re-writing this whole text block for LLVM 12 when the time comes depending on the status of Flang at that time.

[richard.barton.arm]

Looks like I committed this without the link text as 69230e7

flang/docs/ReleaseNotes.md

+# Flang 12.0.0 (In-Progress) Release Notes
+
+> **warning**
+>
+> These are in-progress notes for the upcoming LLVM 12.0.0 release.
+> Release notes for previous releases can be found on [the Download
+> Page](https://releases.llvm.org/download.html).
+
+## Introduction
+
+This document contains the release notes for the Flang Fortran frontend,
+part of the LLVM Compiler Infrastructure, release 12.0.0. Here we
+describe the status of Flang in some detail, including major
+improvements from the previous release and new feature work. For the
+general LLVM release notes, see [the LLVM
+documentation](https://llvm.org/docs/ReleaseNotes.html). All LLVM
+releases may be downloaded from the [LLVM releases web
+site](https://llvm.org/releases/).
+
+Note that if you are reading this file from a Git checkout, this
+document applies to the *next* release, not the current one. To see the
+release notes for a specific release, please see the [releases
+page](https://llvm.org/releases/).
+
+## Known Issues
+
+These are issues that couldn't be fixed before the release. See the bug
+reports for the latest status.
+
+ *   ...
+
+## Introducing Flang
+
+Flang is LLVM's Fortran front end and is new for the LLVM 11 release.
+
+Flang is still a work in progress for this release and is included for
+experimentation and feedback.
+
+Flang is able to parse a comprehensive subset of the Fortran language
+and check it for correctness. Flang is not yet able to generate LLVM IR
+for the source code and thus is unable to compile a running binary.
+
+Flang is able to unparse the input source code into a canonical form and
+emit it to allow testing. Flang can also invoke an external Fortran
+compiler on this canonical input.
+
+Flang's parser has comprehensive support for:
+ * Fortran 2018
+ * OpenMP 4.5
+ * OpenACC 3.0
+
+Interested users are invited to try to compile their Fortran codes with
+flang in and report any issues in parsing or semantic checking in
+[bugzilla](https://bugs.llvm.org/enter_bug.cgi?product=flang).
+
+### Major missing features
+
+ * Flang is not supported on Windows platforms.
+
+## Using Flang
+
+Usage: `flang hello.f90 -o hello.bin`
+
+By default, Flang will parse the Fortran file `hello.f90` then unparse it to a
+canonical Fortran source file. Flang will then invoke an external
+Fortran compiler to compile this source file and link it, placing the
+resulting executable in `hello.bin`.
+
+To specify the external Fortran compiler, set the `F18_FC` environment
+variable to the name of the compiler binary and ensure that it is on your
+`PATH`. The default value for `F18_FC` is `gfortran`.
+
+When invoked with no source input, Flang will wait for input on stdin.
+When invoked in this way, Flang performs the same actions as if
+called with `-fdebug-measure-parse-tree -funparse` and does not invoke
+`F18_FC`.
+
+For a full list of options that Flang supports, run `flang --help`.
+
+## Additional Information
+
+Flang's documentation is located in the `flang/docs/` directory in the
+LLVM monorepo.
+
+If you have any questions or comments about Flang, please feel free to
+contact us via the [mailing
+list](https://lists.llvm.org/mailman/listinfo/flang-dev).

flang/docs/ReleaseNotes.rst

-========================================
-Flang 11.0.0 (In-Progress) Release Notes
-========================================
-
-.. contents::
-   :local:
-   :depth: 2
-
-.. warning::
-
-   These are in-progress notes for the upcoming LLVM 11.0.0 release.
-   Release notes for previous releases can be found on
-   `the Download Page <https://releases.llvm.org/download.html>`_.
-
-Introduction
-============
-
-This document contains the release notes for the Flang Fortran
-frontend, part of the LLVM Compiler Infrastructure, release 11.0.0. Here we
-describe the status of Flang in some detail, including major
-improvements from the previous release and new feature work. For the
-general LLVM release notes, see `the LLVM
-documentation <https://llvm.org/docs/ReleaseNotes.html>`_. All LLVM
-releases may be downloaded from the `LLVM releases web
-site <https://llvm.org/releases/>`_.
-
-Note that if you are reading this file from a Git checkout, this document
-applies to the *next* release, not
-the current one. To see the release notes for a specific release, please
-see the `releases page <https://llvm.org/releases/>`_.
-
-Known Issues
-============
-
-These are issues that couldn't be fixed before the release. See the bug reports for the latest status.
-
-- ...
-
-Introducing Flang
-=================
-
-Flang is LLVM's Fortran front end and is new for the LLVM 11 release.
-
-Flang is still a work in progress for this release and is included for
-experimentation and feedback.
-
-Flang status
-------------
-
-Flang is able to parse a comprehensive subset of the Fortran language
-and check it for correctness. Flang is not yet able to generate LLVM IR for
-the source code and thus is unable to compile a running binary. 
-
-Flang is able to unparse the input source code into a canonical form and emit
-it to allow testing. Flang can also invoke an external Fortran compiler on this
-canonical input.
-
-Flang's parser has comprehensive support for:
-- Fortran 2018
-- OpenMP 4.5
-- OpenACC 3.0
-
-Major missing features
-----------------------
-
-- Flang is not supported on Windows platforms.
-
-Using Flang
-===========
-
-Usage: ``flang hello.f90 -o hello.bin``
-
-Flang will parse the Fortran file ``hello.f90`` then unparse it to a canonical
-Fortran source file. Flang will then invoke an external Fortran compiler to
-compile this source file and link it, placing the resulting executable
-in ``hello.bin``.
-
-To specify the external Fortran compiler, set the ``F18_FC`` environment
-variable to the name of the compiler binary and ensure it is on your ``PATH``.
-The default value for ``F18_FC`` is ``gfortran``.
-
-When invoked with no source input, Flang will wait for input on standard in.
-When invoked in this way, Flang performs the same actions as if called with
-``-fdebug-measure-parse-tree -funparse`` and does not invoke ``F18_FC``.
-
-For a full list of options that Flang supports, run ``flang --help``.
-
-Additional Information
-======================
-
-Flang's documentation is located in the ``flang/docs/`` directory in
-the LLVM monorepo.
-
-If you have any questions or comments about Flang, please feel free to
-contact us via the `mailing
-list <https://lists.llvm.org/mailman/listinfo/flang-dev>`_.