Responses 0.13.0

• responses.upsert() was added. This method will add() a response if one has not already been registered for a URL, or replace() an existing response.
• responses.registered() was added. The method allows you to get a list of the currently registered responses. This formalizes the previously private responses.mock._matches method.
• A more useful __repr__ has been added to Response.
• Error messages have been improved.