Exceptions are irrecoverable when using `get_resource(..., iterate=True)`

[bmwilly]

Since item_iterator returns an empty iterator when an exception is encountered, there is no way to recover the HTTP error that was raised:

This behavior is confusing and makes code difficult to debug. I think in this case, item_iterator should just raise the exception that occurs.

[bmwilly]

Going even further, I think a bad response should always be raised, instead of having send_signed_request sometimes return a dict and sometimes return a requests.Response with a bad status code. In my opinion, being explicit is better than silently returning bad Responses, None, or empty generators. My solution for this is at #12.