radial-gradient() proposal

I'm finally happy with my radial-gradient() syntax.  You can view it
at http://www.xanthir.com/:4bhipd (scroll down past the
linear-gradient() examples).

Highlights are reusing *all* of the infrastructure from
linear-gradient (changing only the default values for <bg-position>
and <angle>), and then adding a second argument which takes two
keywords defining the shape and size of the gradient.  I think this
syntax will cover a large majority of radial gradient uses on the web
(unfortunately, radial gradients are much less common due to them
requiring much larger files), while being simple and easy to
understand and write.  Much thanks to David Perrell for giving me the
arguments that inspired this syntax.

Making examples for radial gradients is substantially more difficult
in GIMP than for linear gradients, so instead I'll be putting together
a generator for them this weekend, and will have examples
live-generated from the syntax afterwards.

~TJ