- open up some private api:
  DelegateParser is public now
- open up some private api: predicate(int, Function, String) allows the creation of custom parsers
- drop the deprecated Result.result message, instead use Result.value
- cleanup result context
- more comments for Token class
- renamed private method _parse(Contet) to parseOn(Context) so that parser classes can be created outside the library
- added @override annotations for more checking in Parser hierarchy