Added `Em.O` (shorthand for `Ember.Object.create`)

I'm not sure if this is something you want in the framework, but I find this syntax a lot nicer when creating a lot of objects:

```
[
  Em.O({
    name: 'Tarzan'
  }),
  Em.O({
    name: 'Jane'
  }),
]
```

= :yum: 

vs.

```javascript
[
  Em.Object.create({
    name: 'Tarzan'
  }),
  Em.Object.create(({
    name: 'Jane'
  }),
]
```

= :weary: 

It's like `Em.A`, but for objects.