Added _ to the parameter name regex.
Allow whitespace after token value.
Allow numbers in parameter types (e.g. int64).
Added OpenGL 4.2 and 4.3.
Added support for asynchronous, context-local callback functions.

The current implementation requires manually coding the callback function
Java and C code. It should be possible to merge Callback with CallbackType/CALLBACK_DATA
in the future but seems like too much effort for little benefit right now.