title: SDWebImage - Method for performing tasks when setImageWithURL completes loading
body: <p>Just like the title says.  Given:</p>
  
  <pre><code>[imageView setImageWithURL:[NSURL URLWithString:imageurl]];
  </code></pre>
  
  <p>What is the best way to perform tasks once the image is loaded (or pulled from the cache) and displayed?</p>