Updates to Racket lexer:

- Actually the \u03BB lambda char does work fine inside %w() with the
  others.
- Since Racket allows identifiers to consist of nearly anything,
  instead of describing what they are, describe what they are _not_.
- Handle quasiquote as well as quote.
Merge pull request #87 from greghendershott/racket-lexer-ids

Updates to Racket lexer