Simpler provider set handling through reflection

[tjdett]

Sets can be now be configured by having a :set attribute, or by having proper set models that relate back to the provider model.

Overriding Provider.find should no longer be necessary, which avoids the possibility of messing up resumption token behaviour.

[travisbot]

This pull request passes (merged 8c2efbf0 into 04ad0daf).

[tjdett]

@cbeer While I could merge this myself, I'd appreciate any feedback you might have on this pull-request.

It's a reasonably large change to the way ActiveRecordWrapper works, though it should produce the same behaviour for existing code.

[cbeer]

looks good to me (although I've never used the ARWrapper, so it's really your call). Does this change require a minor version bump, do you think?

[tjdett]

It does add new backwards-compatible behaviour, so assuming we're using semantic versioning it does require a minor version bump.

I'd give it a few days to see if something of similar size comes along, after which I think it would be worth bumping to 0.3.0.

[cbeer]

+1