title: Socket.io event listening on a specific room
body: <p>I'm not sure it is possible, but I really need that feature.
  Can I do something like:</p>
  
  <p>client side</p>
  
  <pre><code>sio = io.connect(url);
  sio.to('room1').on('update', function(roomName) {
      console.log(roomName);
  });
  </code></pre>
  
  <p>Which will be triggered whenever an update event is emitted to 'room1'?</p>
  
  <p>server side:</p>
  
  <pre><code>sockets.to('room1').emit('update', 'room1');
  </code></pre>