title: Load images from NSURL async with RestKit
body: <p>Is there a wrapper or some sort of built-in functionality available in <code>RestKit</code> to load a <code>UIImage</code> from an <code>NSURL</code> asynchronously using callbacks or blocks? I could not find such a method in the <code>RestKit</code> docs. If there is not, what is a good strategy for implementing lazy loaded async images from <code>NSURL</code> <em>using</em> <code>RestKit</code> as much as possible?</p>