Better Subscription

Subscriptions need to be implemented.

They can be that easy:
```js
var onCommentsAdded = graph.subscribe`{ commendAdded { user {name}, text } }`

onCommentsAdded(function (data) {
  console.log(data.user.name)
})
```

And can be unsubscribed.
```js
var onCommentsAdded = graph.subscribe`{ commendAdded { user {name}, text } }`

onCommentsAdded.unsubscribe()
```