Added the reject for keywords mechanism in the new parser.
  - the grammar generator takes as arguments a set of all tokens found in the definition
  - when finding a Token declaration it compares all tokens to see which one overlap and add them as an exception to the matcher
  - added a regression test which compares the output and err of krun
  - added the AmbFilter at the end of the new parser.
Addressing Dwight's comments.
  - moved rejects from PrimitiveState into RegExState
  - added a few more examples to better test corner cases.
Merge pull request #421 from kframework/reject-keywords

Added the reject for keywords mechanism in the new parser.