title: backbone.js set model attribute inner field
body: <p>I want to set an attribute of a backbone.js model, but only an inner field rather than the entire field.</p>
  
  <p>Example code might be:</p>
  
  <pre><code>model.set('user.avatar', 'img')
  </code></pre>
  
  <p>Anything I can do?</p>
  
  <p>Thanks</p>