Expose JSONAPI::ResourceSerializer#attribute_hash ?

Thanks for all the work on this gem. I've been using it for a new project and I really enjoy it.

For a project I'm currently working on, I have a Song model that has_one :embed. I don't want to expose the Embed model as part of the REST API. I always want to include the attributes of the embed in the response.

The JSON API format document explicitly states that says that attributes "may contain any valid JSON value" and that "complex data structures involving JSON objects and arrays are allowed as attribute values."

I propose that models specified as attributes in a resource should be serialized simply, using #attribute_hash.

For example, this is what my JSON looks like if I simply add :embed as an attribute to my SongResource

"embed": {
  "id": 1,
  "identifier": "1101",
  "site": "youtube",
  "art_content_id": 1,
  "art_content_type": "Song",
  "created_at": "2015-09-04T19:55:41.596Z",
  "updated_at": "2015-09-04T19:55:41.596Z"
}

If it was passed through the serializer, this is what I would get. (this is what I want)

"embed": {
  "identifier": "1101",
  "site": "youtube"
}

Right now, I can do this by manually with code like this in my SongResource

def embed
  resource = JSONAPI::Resource.resource_for @model.embed.class.to_s.underscore
  serializer = JSONAPI::ResourceSerializer.new resource
  serializer.send :attribute_hash, resource.new(@model.embed)
end

If you would be willing to consider a feature like this, I would be happy to put together a pull request for it

Beginne damit, JSONAPI::ResourceSerializer und seinen privaten Einstiegspunkt attribute_hash zu lesen, und vergleiche anschließend, wie die Attribute und Beziehungen von SongResource derzeit serialisiert werden. Bestätige, dass ein eingebettetes Modell als verschachtelte Attribute serialisiert werden kann, mit den angeforderten identifier- und site-Feldern und ohne Embed als separate Ressource offenzulegen.