Improve Parser: Use the Clang API

I'm in the process of doing this right now. Currently, the following issues exists with the approach I'm taking:

• Preprocessor directives are not supported: This is fixable, because Clang can be made aware of those, but it doesn't by default. I'll leave this for later.
• Normal comments cannot be read: Unless I've missed some Clang flag, non-doc comments are completely ignored. I'm not sure this is a big deal, but nonetheless, it's different from the current behavior.