Add ability to opt out of raising errors on non 2xx responses

[adherr]

In our API we occasionally encounter dead links. I would like a version of Representation#related that does not raise when I ask it to reify a dead link. What it should return is interesting.

We return HAL bodies with most errors, and I would like access to that and possibly the response code. Maybe an ErrorRepresentation that acts like a real Representation, giving reasonable responses to the public methods, but that includes details of the error?