Simplify node definition

I'm proposing a simpler way to define a node using Node.create()

Example: creating a node for component classes Point & energy:
```javascript
var PlayerNode = Ash.Node.create({
    point: Point,
    energy: Energy
});
```

This has the same effect as:
```javascript
var PlayerNode = Ash.Node.extend({
    point: null,
    energy: null,

    types: {
        point: Point,
        energy: Energy
    }
});
```

I tested it on `ashjs-asteroids-example` (on branch `simple-nodes`) and it works so far. See the commits at https://github.com/abiyasa/ashjs-asteroids-example/commit/f7ed62b397a5f246511b0162b0555fd7d141cfdf