Documentation looks much nicer now (or at least more familiar).
Test cases become ugly because we need to double the escape in
strings. Also escaping requires \"\\" which in a Scheme string
gets written \\"\\\\". Consider \\ as a shortcut (which is still
\\\\ in a string).
This is much faster (in chibi) and more concise than case-lambda. Also adding
(chibi optional) for the let-optionals and opt-lambda variants.
Still need to add let-keywords*.
