Ember.Inflector: Ember.String#pluralize Ember.String#singularize

(cc @wycats)

Should have rails inflector parity, as to work out-of-the-box with AMS.
This does mean it brings along some railsisms such as the crazy `cow` -> `kine` pluralization.

With rules:
```
Original: 1.35KB gzipped (4.01KB uncompressed)
compiled: 945 bytes gzipped (2.16KB uncompressed)
```

Without rules:
```
810 bytes gzipped (2.44KB uncompressed)
401 bytes gzipped (795 bytes uncompressed)
```