mcc_parse minor refactoring

This splits the giant handle_buffer function into smaller parts that are easier to be parsed.

One thing that feels clunky, is that each funtion takes so many arguments, 2 of which element and self.cap are mainly used for logging.

Another weird thing is that currently every function takes both &self but also &mut State which is in fact self.state. Most of the methods could probably be implemented for State directly