filtering header draft rev 31

I've just edited the miller-et-al filter header document, which you can
find at http://millenix.zemos.net/asrg-filtering/

Changes are a fleshing out of the introduction, design goals and
design requirements sections only. The general gist of it is that
the header is composed of independent attribute/value pairs
in a single header record. Please comment as necessary on this list.

I haven't yet worked on section 4, which lists the allowable
attributes and their format. I'd like to request everybody to
suggest any attributes they feel would be a good idea, and what
those should contain. The actual naming is not too important for now, 
but it would be good to have a large sample of possibilities to give
better shape to the design requirements. 

Remember that this document is in the early draft stage, and can
change radically yet.

-- 
Laird Breyer.