Language document update

Eric and I have been working on the language document and will continue to
do so.

    http://www.w3.org/2001/sw/DataAccess/rq23/

This is still incomplete. The goal of the document is to meet the needs of
someone wanting a complete description of the language and also to define
the language in precise terms.

We would like comments on any area but especially: 

+ Sections 2,3,4, which start on SELECT, constraints and optionals.
+ document structure
+ approach of mixing examples and formal description.

	Andy