Catch non-JSON errors in the Go SDK

[Swimburger]

Most errors return a JSON HTTP body that looks like this:

{
  "status": "error",
  "error": "the error message"
}

However, there are bugs in the API where it sometimes returns errors as plain text or HTML.
The Go SDK needs to be able to handle this gracefully and return the full HTTP body to the user somehow so they can debug the issue.