Clojurians Log v2

Following up on this, the response map reference doc has been updated (http://pedestal.io/reference/response-map). Thanks @isak for the initial PR. What is considered a valid response depends on which part of Pedestal is currently in question. The servlet integration impl abides but the Ring contract (`:status`, :headers are required). The default not-found interceptor uses a looser contract (only :status required). This was intentional since chain providers may vary.

Ah, I see. Nice!