code: function setup(opts) {
    if (GestureDetector.READY) {
      return;
    }
  
    // find what eventtypes we add listeners to
    Event.determineEventTypes();
  
    // Register all gestures inside GestureDetector.gestures
    Utils.each(GestureDetector.gestures, function(gesture) {
      Detection.register(gesture);
    });
  
    // Add touch events on the document
    Event.onTouch(GestureDetector.DOCUMENT, EVENT_MOVE, Detection.detect, opts);
    Event.onTouch(GestureDetector.DOCUMENT, EVENT_END, Detection.detect, opts);
  
    // GestureDetector is ready...!
    GestureDetector.READY = true;
  }
docs: setup events to detect gestures on the document
  this function is called when creating an new instance
  @private