Updated Versioning finding(s) available

Dated 20070518, they are at
http://www.w3.org/2001/tag/doc/versioning
http://www.w3.org/2001/tag/doc/versioning-strategies
http://www.w3.org/2001/tag/doc/versioning-xml

I've done Rhys' and Norm's comments, add the subst group example, added
mention of version id mapping, and split part 1 into termionology and
strategies documents.  Sadly, I also deleted the
version-xml-20070518.xml file but that's something I can redo later.

Cheers,
Dave