code: function Mouse() {
      EventDispatcher.call(this);
  
      this._x = 0;
      this._y = 0;
      this._prevX = 0;
      this._prevY = 0;
      this._deltaX = 0;
      this._deltaY = 0;
      this._isDown = false;
  }
docs: EventDispatcher for mouse events
  @class
  
  @example
  var Window = require('pex-sys').Window;
  var MouseEvent = require('pex-sys').MouseEvent;
  
  Window.create({
  init: function() {
  var mouse = this.getMouse()
  mouse.addEventListener(MouseEvent.MOUSE_DOWN, function(e){ });
  mouse.addEventListener(MouseEvent.MOUSE_UP, function(e){ });
  mouse.addEventListener(MouseEvent.MOUSE_MOVE, function(e){ });
  mouse.addEventListener(MouseEvent.MOUSE_DRAG, function(e){ });
  mouse.addEventListener(MouseEvent.MOUSE_SCROLL, function(e){ });
  }
  })