Support include on RelationshipView endpoints

[jokiefer]

Hi folks,

as described inside the specs 8.2 relationshop views should support including related data.

Furthermore, related resources can be requested from a relationship endpoint:

GET /articles/1/relationships/comments?include=comments.author HTTP/1.1
Accept: application/vnd.api+json

In this case, the primary data would be a collection of resource identifier objects that represent linkage to comments for an article, while the full comments and comment authors would be returned as included data.

Note: This section applies to any endpoint that responds with primary data, regardless of the request type. For instance, a server could support the inclusion of related resources along with a POST request to create a resource or relationship. 

I trial this with my RelationshipView, but it seems to me that including related data is not supported by this package.
Maybe there is a workaround?

[sliverc]

Thanks for reporting. Yes, I see it the same way that this should be possible, but currently it is not. The best way to approach it is first to create a reproducing test and then secondly try to implement it in the renderer. PR is welcome.