Proposed doc for while/until

[David H. Adler]

Note: Proposing to put this *above* repeat/while / repeat/until.

https://gist.github.com/dha/0a0736b9da74a8e61e49

dha
-- 
David H. Adler - <d...@pobox.com> - http://www.panix.com/~dha/
A feature is often a bug with seniority.        - Chip Salzenberg