enable feature negotiation; support server max_rdy_count; better logging
wait 2x heartbeat interval before closing conns:

* user reported issues of producers with no message flow having
  their connections closed (and their message handlers performed
  sometimes long blocking operations).  the problem is that if
  the blocking operation happens just before you expect
  another heartbeat when the ioloop wakes up it fires the timer
  and those conns are closed (even though presumably a heartbeat
  is sitting waiting to be read).