Ember1.0 use attribute name in url for hasmany

Fixes #40.
This uses the attribute name for hasMany relationships instead of the model type.

For a model like this

 ````
App.User = DS.Model.extend({
    username: DS.attr('string'),
    aliases: DS.hasMany('speaker', { async: true})
    favorites: DS.hasMany('speaker', { async: true})
});
````

requesting `user1.get('aliases')` would have caused the URL `/users/1/speaker` to be requested. This PR changes the behavior to use the name of the attribute instead, resulting in a request to `/users/1/aliases`. This also allows for multiple hasMany relationships to exist in a single model and be correctly requested.