title: Is there a way in History.js to know when the back button was pressed
body: <p>I've started to test <a href="https://github.com/balupton/history.js" rel="noreferrer">History.js</a>. After understanding how it works and that there is no <code>popstate</code>, instead there is <code>statechange</code>. I'm looking for a way to differ when the back button of the browser has been pressed.</p>
  
  <p>The reason is that I need to know the URL before the state moved, from the one I'm going to. With the <a href="https://gist.github.com/854622" rel="noreferrer">gist</a> the project includes, only the URL we go to is looked.</p>
  
  <p>I hope the solution is not to track latest URL visited in a global variable.</p>
  
  <p>Thanks</p>