responder now accepts 'word' and 'vocab' as query parameters. The
cont-responder takes the continuation id as a query parameter instead of
part of the url.
added start of a tutorial
added numbers game example
add cont-responder testing functions
minor refactoring of cont-responder
eval-responder now works again!
Changes to parser-combinators:
modify str-head and str-tail usage for their changed stack effects
Chris Double
Slava Pestov