Jingyu Ma

I need to recalculate the position for individual objects after rotating, resizing or zooming. Will check this issue later.

I just tried to add following code to the [demo page](https://github.com/mazong1123/fabric.ext/blob/master/fabricext/demo/events.html), and the double click events are still alive after loadFromJSON: ``` javascript var j = JSON.stringify(canvas.toJSON()); canvas.loadFromJSON(j, canvas.renderAll.bind(canvas)); ```...

@monsur can this detecting logic be absorbed into Cache's constructor so that the user won't worry about choosing storage?