Reworked sections on datatypes and literals

Starting with Brian's comments, and then employing a lot of editorial 
discretion, I've done a major rework on the sections about datatypes and 
literals.

The main goal of this rework was to progressively introduce the concepts, 
so the datatypes section has been moved ahead of literals, and the datatype 
examples have been split across the two sections.

The rework is attached to this message.  It's not very long -- I'm posting 
the two sections to solicit feedback from the group, and make sure I 
haven't distorted the intent in any way.  (There's still an issue of 
requiring a lexical representation for each value [1] outstanding, which I 
haven't got round to addressing yet, so please don't flame me on that just 
yet.)

#g
--

[1] http://lists.w3.org/Archives/Public/w3c-rdfcore-wg/2002Oct/0396.html



-------------------
Graham Klyne
<GK@NineByNine.org>