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.

Nearley tool still needs fixing

Added __slots__ to RulePtr and Token, resulting in significantly lower memory consumption.

As suggested by @drslump.

While optimizing hot spots in a tool I wrote I saw this issue. Changing this to use a for loop granted a minor speed boost to my script.