Ability to override the resource name when calling `Model.api.set()`

There's currently no way to override the resource name without specifying each individual URL. This PR allows you to set the full path to the resource. Example:

```js
angular.module('app', ['ActiveResource'])
  .factory('Post', ['ActiveResource', function(ActiveResource) {

    var Post = function (data) {
      // ...
    };

    Post.inherits(ActiveResource.Base);

    // this will use "posts" as the resource name
    Post.api.set('http://api.faculty.com/posts', true);

    return Post;
    
  });
```