Standardize error handling

[aoberoi]

There needs to be a set of Error types defined and their meaning nailed down so that developers can predictably deal with error conditions.

This will also be subject to an internal API Review.

[aoberoi]

A specific use case where error types are preferable is in #110

[aoberoi]

In #114, the case is made that we should propagate error messages that come from the REST API rather than squelching them and covering them up with a generic message.

The way forward from this point is with an actual API proposal.

[michaeljolley]

Closing as outdated.