Make C++ autodoc pipeline capture the new GPU docs and update version numbers

[suntzu86]

BLOCKING: #344

1. define a __version__ string in moe.__init__.py
2. update version number in docs/conf.py (git grep for 0.1.0) to reference that version string
3. Update contributing.rst to include a note about updating the version string when we do a version bump
4. docs/conf.py add gpu directory and possibly add '.cu' ending
5. docs/doxygen_config add gpu directory and possibly '.cu' ending
6. any other places to add gpu directory?
7. modify docs/cpp_rst_maker.py to read from the gpu directory and handle .cu files

edit: for now, I'm going to just flatten the gpu subdirectory for the purpose of doc'ing. Improving this is the subject of #360