Added predicates
Added binary node types
Improve Combinators
Added binary operators
Improve Grammar class
Added Identifier rule and fix test doubles
Refactored Label to use Identifier
Cleaned up test doubles
Added nodes for grammar and rules
Added last rules to finish grammars
Added combinator MatchedString
Improved combinators: returning arrays and null and stuff
Fixed rule factories to use new combinators
Updated specs
Move Grammar rules from constructor to adder
We can now parse grammars with a parser
Started work on grammar tree visitor
Started work on visitor for generating combinator parsers
Finished grammar node visitor
Added predicate combinators