Dynamically reload asset files when they change

All examples work.
Also tested Swooop, and a couple of other games and they all work.
I am kindof scared to do this though. Because it means that whenever you set an asset property you will raise events and these events are there only for reloading assets basically. So if you set asset.resource to something somewhere temporarily or whatever that is going to raise events which might have quite complicated handlers. That's why I added a 'set' method so that you are aware that you will raise events when you call it.