[XeTeX] xetexref updated

[Will Robertson]

Hello,

At long last I've updated the xetex-reference documentation:
   <http://scripts.sil.org/svn-public/xetex/TRUNK/texmf/doc/xetex/ 
xetexref>
It's still very terse, but contributions are gladly accepted :) Even  
single sentences in some places would improve the document and make  
my life easier.

This version adds the extended maths primitives and the new char  
class primitives. I haven't documented the Graphite additions,  
though. If I don't receive any suggestions or corrections on this  
version I'll (finally) upload it to CTAN, as well.

Have fun,
Will