title: Eloquent sortBy - Specify asc or desc
body: <p>Trying sort my eloquent collection:</p>
  
  <pre><code>$collection-&gt;sortBy('field');
  </code></pre>
  
  <p>There is no information in Laravel 4's docs on how to choose descending or ascending for this sort method.</p>
  
  <p>Is it possible?</p>