[cairo] [RFC] Color space API (partial proposal)

[Bill Spitzak]

I do not think cairo_color_t is necessary, just the cairo_color_space_t. 
I would prefer to set colors with an api like this:

	cairo_set_source_color(cairo_t*, cairo_color_space_t*, void* data)

The reason is that the "data" is quite likely already in a memory 
structure with the correct format (such as an array of float).

This also makes the emulation of the existing color api trivial without 
allocating any temporary objects.

I also feel it may be possible to unify images and colors with this, 
something I consider fairly important. A "color" is just a 1x1 image. We 
could make cairo_color_space_t be a full description of the pixels in an 
image.