First draft of the blending and compositing spec

All,

Nikos and I have created a first pass at a compositing and blending spec
and posted it here:
https://dvcs.w3.org/hg/FXTF/rawfile/tip/compositing/index.html

The section on compositing needs more depth, but I think the blending and
specification section are ready for a first review.
We will present this during next week's FX face-to-face meeting along with
some prototype implementations.

Let us know what you think.

Thanks!
   Rik Cabanier
   Adobe Systems, Inc