Integrate the new Responsive Breakpoints functionality?

Excited about this: http://cloudinary.com/blog/introducing_intelligent_responsive_image_breakpoints_solutions

What's the plan for integrating this into the gem? Maybe a new `process` directive?

Ideally the view would have a helper to generate either `srcset` attributes on your `` tag, or maybe a new `source_tag` helper that generates the whole thing for you, including a fallback `` tag for dumb IE?