New error handling system

[zayfod]

Currently pyfranca's error handling is rudimentary. Whenever lexer, parser, or processor errors are detected an exception is raised and further processing stops.

Error handling has to be reworked to allow keeping a list of detected errors (objects) as part of a processor. Processing should stop only when fatal errors are detected. Simpler lexer and parser errors should just be detected and added to the list but processing should continue.