[JDEV] First cut at a DTD

[Jeremie]

> New version attached.  Revised per comments.

Excellent... I just checked this into the distribution, as
docs/protocol/jabber.dtd

I'm wondering what you think about making this even a bit more generic, so
that it inclusively covers all of the Jabber protocol pieces, the client
and server, in one package.  All it would require would be adding a few
more attributes/tags in certian places, most of the important
parts(messages/status)  are the same.   Creating a second DTD would be
just as easy, just not sure which is more appropriate.

Jer