Canvas Floating Point Color Values Propoal

As discussed in the previous call, I've separated floating point pixel
values from HDR canvas capabilities.

The following document is that proposal.
https://github.com/w3c/ColorWeb-CG/blob/master/canvas_float.md

Please provide any feedback you have on the proposal. I will be trying to
get this landed in the HTML spec first, and then introduce the HDR canvas
proposal separately.