Reflect

The Reflect global is, as far as I know, a part of the ES6 spec. I was a bit surprised not to find it in the es6-shim. Is there any reason as to why it isn't? If not, I'd consider giving it a go.

I'd like to use this PR to discuss Reflect implementation.
Array Iterator not suitable for `Reflect.enumerate`:
```javascript
var O = {q: 1, w: 2, e: 3};
var I = Reflect.enumerate(O);
delete O.w;
Array.from(I); // => ['q', 'w', 'e'], expected ['q', 'e']
```