Implemented ord in terms of negative lookahead
Brings even more into alignment with how PEG parsers work.
Minor efficiency change
Better handling of nested negatives
Minor edits
Added alt-or-ord nodes to grammar
Trying to add error handling
Trying to add error handling 2
Trying to add error handling 3
Working on core interface
Broke up gll namespace into combinators and combintors-private
Added pretty-printing of errors
Added errors.clj file