Return raw errors

[seanmor5]

This is just a proposal, but basically I have a reasonably complex workflow that requires a lot of calls to the OAI API. Because of this, I'm running into rate limit issues that I would like to handle by adding some retries with backoff functionality. I can just match on {:error, _}, but having the raw errors would make things a bit easier because I can handle the specific case where the API returns a rate-limit exceeded error and do the retries in that case. Thoughts?