Related resources are not fetched via their own link

[anuragagarwal561994]

There can be a possibility that related resources might have different links, like if A has a relation B.

A {
    "data": {
        ...
        "relationships": {
            "B": {"data": {...}, "links": {"self": "prefix/B"}}
         }
    }
}

B should thus be fetched by its link and not like the regular fetch_by_id.