- `user_repr` is now a method
- Fix for python 2.7
- excepts -> expected

rename LexerConf.terminals to LexerConf.tokens
Make Exception message generation lazy
Made a few classes new-style

- Refactored lexer interface into LexerConf
- Lexer now compiles regexps only when used (especially useful for ContextualLexer)
- Lexer now doesn't validate on deserialize (noticable speedup)

* 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.

Big Thanks to Seth G of the mappyfile project for financing this feature!

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