TODO #177

WIP Refactor Descriptor:

• Create accurate TypeMap for C, C++, JavaScript, and Emscripten.
• Get access to struct information to finish git_tree_entry.
• Clean up generate/* files.
• All pre-existing tests should pass.

Future branches:

• Introduce code coverage and better test analysis.
• Prebuilt binaries.
• Remove docs (also from gitignore).
• Mocha / Istanbul test suite integration.
• Move index.js to lib/nodegit.js.