Make go to definition open another source file in a split window.
If some other plugin has already loaded libclang, don't fight with it.
Use underscore instead of dash in clang_tools, so it can be imported in
Python.
Splitting out the non-vim-specific stuff into its own Python module.
Beginning to make find_definition search across translation units.

This is not used in the vim plugin, yet.
Add gitignore.
Beginning CrossTUIndex, which will hold a group of TUs and cached
information about them.
Switch to CrossTUIndex for storing the tus. This enables
cross-translation unit "find definition".
Refactor find_definitions so it's just a member function.