Feature/fix perf

/to @ritch 
/to @bajtos 

Here are a few patterns I use:

1. Convert array.forEach(fn) to for(var k = 0; k < keys.length; k++) {...};
See: http://jsperf.com/fast-array-foreach

2. Avoid Object.defineProperty()
See: http://jsperf.com/object-defineproperty-vs-definegetter-vs-normal/21

3. Avoid array.indexOf() 
Initialize `__data` in `initProperties` and define the non-enumerable property (without a value) in during model definition.

```js
Object.defineProperty(ModelClass.prototype, '__data', {
  enumerable: false,
  configurable: false
});
```