Updated/reorganized spec

As we agreed, http://www.textuality.com/sgml-erb/WD-xml.html is now
a stub/hub document, pointing to the base XML spec, WD-xml-lang.html
and our new baby, WD-xml-link.html.  WD-xml-lang.html remains un-updated
since November (bad, *bad*, editors!).  WD-xml-link.html is now dated
March 5, has been updated throughout for terminology, and sections 1 
through 4 have been updated in line with ERB decisions over recent weeks.

Input, as always, gratefully accepted, everything including general
organization, style, presentation, and of course accuracy.  As for the
material design issues, if at all possible could we keep to the numbered
discussion headings in order to keep this runaway omnibus headed in
more or less the right direction.  In offering editorial input, please
use consideration in deciding whether to send input to the mailing list
(recommended for technology issues) or just to Steve and me (recommended
for style/typography/etc).

Cheers, Tim Bray
tbray@textuality.com http://www.textuality.com/ +1-604-708-9592