[Enhancement] Adding moment computed fixes #6

This PR is dependent on #9.  Will squash once you thumbs up and merge #9 .
the set operation seems to be very complex as often it will be via raw user input. I think the get can be simple, but I am concerned conflating it with the set.

Some related ideas, maybe it will spark some ideas.

rather then implicit setter:

```js
fullName: Ember.computed(function(a,b) {
  if (arguments.length > 1) {
    // setter
  } else {
    // getter
  }
})
```

implicit should become `get` only, and a pojo argument to computed would optionally indicate a setter.

```js
fullName: Ember.computed({
   get: function() { ... } // still only a getter
})
```

but then, its obvious when we have an explicit setter.

```js
fullName: Ember.computed({
   set: function() { ... }, // the setter
   get: function() { ... } // the getter
})
```

and with es6 (and now esnext)

```js
fullName: Ember.computed({
   set () { ... }, // the setter
   get () { ... } // the getter
})
```

but the reason i bring this up here, is I wonder if it would be nice to split the date-parsing into 2 distinct helpers.

```js
fullName: Ember.computed({
   set: function() { 
     // more complex logic to handle crazy/partial user input
   },
   get: formatDate('dateAsString', 'MM/DD/YY')
})
```

Another note, recently I have been often preferring to receive use input as actions + values rather then being 2 way data bound (yes crazy i know). But it often has a nice simplifying effect.