Features/json api format

BREAKING CHANGES:

`api#set` method now defaults to parameterizing the updateURL and deleteURL with the primary key:

```
Post.api.set('http://api.faculty.com')
Post.api.updateURL => 'http://api.faculty.com/:id'
Post.api.deleteURL => 'http://api.faculty.com/:id'
```

Also adds `api#format` method to append to requests:

```
Post.api.set('http://api.faculty.com').format('json');
Post.showURL => 'http://api.faculty.com/posts/:id.json'
```

Note: this change does not yet parse Mimetypes alternate to JSON. It only updates requests for APIs that require the Mimetype to be specified (e.g. out-of-the-box Rails APIs).