[sancov] sancov tool documentation

[kcc]

LGTM, please commit after html_cov_report is ready.

docs/SanitizerCoverage.rst

 numbers:
 
 .. code-block:: console
 
     % sancov.py print a.out.22679.sancov a.out.22673.sancov 2> /dev/null | llvm-symbolizer --obj a.out
     cov.cc:3
     cov.cc:5
 
+Sancov Tool
+===========
+
+A new experimental ``sancov`` tool is developed to process coverage files.
+The tool is part of LLVM project and is currently supported only on Linux.
+It can handle symbolization tasks autonomously without needed any extra 
+support from environment.
+
+.. code-block:: console
+
+    USAGE: sancov [options] <action> <filenames...>
+
+    Action (required)
+      -print                    - Print coverage addresses
+      -covered-functions        - Print all covered funcions.
+      -not-covered-functions    - Print all not covered funcions.
+      -html-report              - Print HTML coverage report.
+
+    Options
+      -blacklist=<string>         - Blacklist file (sanitizer blacklist format).
+      -demangle                   - Print demangled function name.
+      -obj=<string>               - Path to object file to be symbolized
+      -strip_path_prefix=<string> - Strip this prefix from file paths in reports
+
+
+Automatic HTML Report Generation
+================================
+
+If ``*SAN_OPTIONS`` contains ``html_cov_report=1`` option set, then html
+coverage report would be automatically generated alongside the coverage files.
+The ``sancov`` binary should be present in ``PATH`` or
+``sancov=<path_to_sancov`` option can be used to specify tool location.
+
+
 How good is the coverage?
 =========================
 
 It is possible to find out which PCs are not covered, by subtracting the covered
 set from the set of all instrumented PCs. The latter can be obtained by listing
 all callsites of ``__sanitizer_cov()`` in the binary. On Linux, ``sancov.py``
 can do this for you. Just supply the path to binary and a list of covered PCs: