[Feature Request] Adding header file for url_parser.pyx, and parser.pyx

[raceychan]

I would like to be able to use/extend classes/functions from parser.pyx and url_parser.pyx, however, currently I am not able to use it since its missing pxd files.

I can submit a PR if this is something you guys would agree with.

[raceychan]

I did a quick scan through on parser.pyx, it seems that it works by receiving a python object, and inspect on the object to see what are the implemented callbacks, wouldn't it be easier and faster for the protocol object to just inherit from httptools.parser.HttpParser?

we don't need to do all those

if self._proto_on_xxx is not None:
    self._proto_on_xxx()