Support Windows & cl.exe/clang-cl.exe

[helmesjo]

This PR adds support for Windows (mainly dealing with \ ), and also adds cl.exe & clang-cl.exe (.exe extension optional).

Verified on a big project of mine (thousands of files), and still works fine on Linux/Macos with gcc & clang/appleclang.

Todo:

• Update versions in requirements-devel.txt, some of them seem broken but latest versions of all install just fine (unrelated to this PR and should be fixed separately).
• Fix failing tests in master (unrelated to this PR and should be fixed separately).
• Add tests for cl.exe & clang-cl.exe.
• Minimize regex for build/argline, probably quite OP for this use-case (see SO link where that part was taken from).

If anyone wants to chip in that be swell. Working with a broken finger and arm cast so kinda suboptimal.

If you don't want to wait for this PR to be completed (if ever, this repo seems pretty abandoned), you can install it directly using:
pip install git+https://github.com/helmesjo/compiledb@support-cl-clang-cl
Work out-of-the-box on Windows and with MSVC. If not, let me know.

[GitMensch]

Do you mind squashing the last two commits into one?

[helmesjo]

@GitMensch Sorry for the delay, missed your comment. Squashed the commits.