code: function MoveBy (opts) {
      MoveBy.superclass.constructor.call(this, opts)
  
      this.delta = util.copy(opts.position)
  }
docs: @class
  Animates moving a cocos.node.Node object by a given number of pixels
  
  @memberOf cocos.actions
  @extends cocos.actions.MoveTo
  
  @opt {Float} duration Number of seconds to run action for
  @opt {geometry.Point} position Number of pixels to move by