python2 is EOL, swith shebang to python3

Signed-off-by: Changqing Li <changqing.li@windriver.com>

This fixes a continuous build
(https://travis-ci.org/github/google/perf_data_converter/jobs/714589290)
running on Ubuntu 16.04 using gcc-4.8.

git-subtree-dir: doc
git-subtree-mainline: 44058714
git-subtree-split: 8411df71

GCC gives an implicit-fallthrough warning (included in -Wextra). C++17 has the [[fallthrough]] attribute, and GCC7+ has __attribute__ ((fallthrough)), but I didn't want to require either so I refactored the switch into if statements.

Bazel genrules require a msys shell to execute
shell commands. Replace the genrules with a
simple C++ regex replacement binary.

Fixes #303.

INFO: From Compiling external/com_github_gflags_gflags/src/gflags_completions.cc:
external/com_github_gflags_gflags/src/gflags_completions.cc:459:16: warning: code will never be executed [-Wunreachable-code]
      DVLOG(3) << "Result: most-common match";
               ^~
1 warning generated.

```
gflags.h(226): warning: attribute "visibility" does not apply here
```

The visibility attribute applies to symbols like functions and variables. A definition of an enumeration type that doesn't contain a variable name doesn't create any symbols.

If the workaround in issue #43 is used along with the define of
STRIP_FLAG_HELP to 1, there would be a wrong "No modules matched"
message been print at end of the usage message.

That's because we continue the loop if we see strip flag help value and
never set the `found_match` flag to true even if we found a match.

By moving the set statement above the continue, we can avoid this wrong
message.

Found with readability-redundant-string-init

Signed-off-by: Rosen Penev <rosenp@gmail.com>

Deprecated with C++14.

Found with modernize-deprecated-headers

Signed-off-by: Rosen Penev <rosenp@gmail.com>

More consistent with other pkgconfig files.

No functional difference.

Add missing @ to cmake-config.in

Add missing @ to cmake file