title: Return/invoke the NotFoundHandler in slim framework
body: <p>Im trying to redirect to the 404 page. Laravel has an option to to this with <code>abort(404)</code>. </p>
  
  <p>Currently I'm doing </p>
  
  <p><code>return $response-&gt;withStatus(404)-&gt;withHeader('Content-Type', 'text/html')-&gt;write('Page not found');</code></p>
  
  <p>But this doesn't redirect to my "normal" or the app´s standard 404 page.</p>
  
  <p>I have read the <a href="http://www.slimframework.com/docs/handlers/not-found.html" rel="nofollow">docs</a>, but how to I invoke the notFoundHandler from wherever in the app?</p>