Unexpected status code treatment

[n8han]

We want to default to non-20x status codes being a fatal error, but this behavior should be obvious to the reader and also obvious how to override it.

[n8han]

We should also anticipate people want to log some portion of the response body when there is an unexpected status. Just the number or an instance of this class is not much context.

[n8han]

I tried adding the handler to the StatusCode class but it wasn't very useful. You have to match against the type of the handler and get it right to do much with it. I think in most cases if people want to handle the non-okay cases they won't use the ok handler, now that it's explicit.