TODO:
  
- support a filter to emit a list of glossary terms used in a post (which might
  be formatted as a sidebox in an article).

- make another filter which discovers candidate glossary terms
  (perhaps any sequence of 3 or more capital letters) and save those
  in a table where the admin "promote" them to glossary term status and
  give them definitions if they are in fact worthy of glossary status.

- change backend storage to 'node' instead of 'term' so that entries may be submitted by anyone, and not just
  taxonomy admins. further, enttries could then be queued, promoted to home page, versioned, etc.

Bugfixes and cleanups to current version which must be done before release:
  * Add complete doxygen comments
  * Fix alphabet bar. It has problems when a term does not start with a letter.
    What to do in UTF8 domain? See also issue 10645. Perhaps only generate
    letters which are actually used?