Delete trailing whitespace in help/Docfiles

Purge on broken links within the (HTML) documentation. This mostly involves
deleting SEEALSO entries (where documentation doesn't exist) but also fixing a
few links.

Also fixed the anchor links in TheoryIndex.html and idIndex.html. In both
cases there aren't any entries starting with the letter "Y".

Docs for the assocs were wrong. Also
Lib.find doesn't exist.

Modifications and some new stuff.

Huge number of check-ins, implementing change to .doc file syntax.
Now the rule for text within braces is that it appears as given, but
that braces must balance. If you want an unbalanced brace, you can use
\lbrace or \rbrace. No existing .doc file uses unbalanced braces.
Also, there is now no need to use \noindent. In fact, doing so
will get you a complaint from the parser. Similarly, use of \ or
{} characters outside of verbatim text blocks will cause griping.
All of the new files have been generated by a parse-then-print process
from the old files, and it's possible there are errors. If you ever
have a spare moment, casting your eye over a random selection of these
might help to find errors.

Fixes to existing docs.

Finished documenting the Lib structure.

New versions of docfiles.