seemingly working parse of compile_commands.json

[cheshirekow]

Not really a pull request. I decided to take a stab at #59 because I would also like to try cldoc with an existing cmake-managed project (many different compile flags for different parts of the build).

Dealing with the compile_commands.json file appears to work as intended, but I get no output from cldoc (empty index.html). If you wouldn't mind taking a look at the diff and let me know if you see anything funky.

[cheshirekow]

FYI: I'm on an ubuntu 14.04 system with clang 3.6. I tried to run this patch with

:~$ LD_LIBRARY_PATH=$(llvm-config-3.6 --libdir) PYTHONPATH=${HOME}/Codes/cldoc \
    python -m cldoc.__init__ generate -- \
   --compile_commands /path/to/my/cmake/project/build/compile_commands.json \
   --output /tmp/cldoc