List of resolver verification errors and error codes

[swcurran]

I thought it would be useful to add a ticket where we can track a list of error conditions in the resolver that are possible and what error codes (or other technique) we can use to surface the error to the caller.

• Log not found.
• etc.

[andrewwhitehead]

So far the Python implementation just uses notFound if the DID log cannot be resolved (404 or other HTTP error), and invalidDid if the processing of the log fails for any reason. The resolution result has both an error code and a message, so the message can be used for additional information.