[racket] pre-announcement for ragg. Request for comments and suggestions

>
> Could it work with parser-tools/lex?
>

Yes.  It's currently undocumented, but yes, you can.  For example, see:

    https://github.com/dyoo/ragg/blob/master/ragg/test/test-simple-arithmetic-grammar.rkt

where it's using lexer-src-pos to provide the source locations.  Note
that you can have lexers return whitespace tokens, which Ragg will
know to ignore during parsing.