[CHANGE] New PreTeXt discussion/announcement groups

[Robert Beezer]

The current mathbook-support group is feeling the burden
of having to fulfill too many requirements: it is used for
announcements of general interest, technical discussions
among developers, and assistance to users having a variety
of issues.

To remedy this problem, we are creating three new newsgroups:
one for each of the items listed above.

Sometime soon, maybe this week, all of you will be subscribed
to the announcement group.  Please keep your membership in that
group because that is the place where you will find out new
PreTeXt features.  That group will be for announcements and
will have very little discussion.

Each of you will have to choose to subscribe to the development
and the support groups.  Please do subscribe, as appropriate to
your interests in (being helpful)/(getting help) and/or
(discussing PreTeXt features)/(implementing PreTeXt features).

The current mathbook-support group will not be deleted,
but once the new groups exist, the most common response will
be to suggest posting to the new group.

Tip-of-the-hat to David Farmer for getting this organized.

Rob, David, Alex