title: Getting changed attribute on change event
body: <p>In this global change event, is there a way I can detect which attribute was changed?</p>
  
  <pre><code>myModel.on('change', function(model) {
    // Which attribute changed?
  });
  </code></pre>
  
  <p>I tried the following:</p>
  
  <ul>
  <li>Using <code>myModel.previousAttributes()</code> but it always returned latest values... I guess it only updates after a server interaction.</li>
  <li>Iterating trough attributes and using <code>myModel.hasChanged(attr)</code> but it always returned false.</li>
  </ul>
  
  <p>It's there a way to accomplish this?</p>