[PATCH] Added doxygen support for the tools of clang-tools-extra repo

[Sean Silva]

  This looks great.

  I just realized that some parts of the doxygen output can be made a bit prettier setting `FULL_PATH_NAMES = YES`, so please change that (see the rationale at <https://github.com/chisophugis/klang/commit/2b7046e6e51e00751a9d9bc2eec67faf5538fa6b>).

  Other than that, this LGTM.

http://llvm-reviews.chandlerc.com/D451