Add support for Sparse Fieldsets #10
Description
Taken from json:api spec
A client MAY request that an endpoint return only specific fields in the response on a per-type basis by including a fields[TYPE] parameter.
The value of the fields parameter MUST be a comma-separated (U+002C COMMA, “,”) list that refers to the name(s) of the fields to be returned. An empty value indicates that no fields should be returned.
If a client requests a restricted set of fields for a given resource type, an endpoint MUST NOT include additional fields in resource objects of that type in its response.
If a client does not specify the set of fields for a given resource type, the server MAY send all fields, a subset of fields, or no fields for that resource type.