Warning: a large cleanup coming soon!

[eidheim]

Main issues: circular includes, forward declarations and the library can be more c++ friendly. TranslationUnit becomes the main class with the following important methods:

clang::CodeCompleteResults get_code_completions(const std::map<std::string, std::string> &buffers, int line_number, int column);
std::vector<clang::Diagnostic> get_diagnostics();
std::unique_ptr<Tokens> get_tokens(unsigned start_offset, unsigned end_offset);

Also going to label all the CX* objects to for instance cx_tu instead of tu_.