title: hammer.js pan limit—how to set boundaries
body: <p>I currently have this code:</p>
  
  <pre><code>var hammertime = new Hammer(canvasContainer);
  var x0, y0;
  hammertime.on('panstart', function(ev){
   x0=stage.position.x;
   y0=stage.position.y;
  });
  hammertime.on('pan', function(ev){
    stage.position.x = x0 + ev.deltaX;
    stage.position.y = y0+ ev.deltaY;
    renderer.render(stage);
  
  });
  </code></pre>
  
  <p>This pans great, but with the current code I can keep panning until the image is off the screen. How do I limit it so the image only goes e.g. half way off the screen before you can't pan in that direction any more? Is there a preset option in Hammer.js for that?</p>