Subject: [Acme] Pull request: clarify error handling

From: Jacob Hoffman-Andrews <[email-masked]>
Date: Wed, 14 Oct 2015 10:35:33 -0700

https://github.com/ietf-wg-acme/acme/pull/17

Previously the language was ambiguous about whether the list of error
types was intended to be exhaustive. This clarifies that clients should
handle unknown error types gracefully. It also adds a new `rateLimited`
error type.