title: How can I convert a date to a UNIX timestamp with Twig?
body: <p>I need to convert a date to a UNIX timestamp in a <a href="http://twig.sensiolabs.org/">Twig</a> template:</p>
  
  <pre><code> &lt;li&gt;{{ user.expired }}&lt;/li&gt;
  </code></pre>
  
  <p>Is there a function in Twig to do it?</p>