Changed dynamic lexer behavior to only match terminals to their maximum length (i.e. greedy match), emulating the standard lexer.

The original dynamic lexer behavior, that attempts to match all appearances of a terminal, has been moved to the "dynamic_complete" lexer.

For example, when applying a terminal "a"+ to the text "aaa":

- dynamic: ["aaa"]
- dynamic_complete: ["a", "aa", "aaa"]

* All exceptions are now under exceptions.py
* UnexpectedInput is now superclass of UnexpectedToken and UnexpectedCharacters,
  all of which support the get_context() and match_examples() methods.

Anonymous tokens would become visible if they had the same value as named tokens.
That's because they are merged for the lexer. But after this change, the rules for
visibility are based on their use in the rule, and not their name or identity.

* Removed the scanless parsing feature (dynamic lexing is king)
* Default LALR lexer is now contextual

It now knows how to resolve ambiguity! And in a memory-efficient way!

Also some issues with python_parser