conn: don't publicly embed net.Conn
conn: s/Stop/Close; CloseRead if no messages in flight upon Close(); refactor
conn: refactor WriteCommand locking and simplify Flush
reader: use new conn.Close
reader: use wg for rdyLoop and lookupdLoop; s/ExitChan/StopChan
reader/writer/conn: conn doesn't take topic/channel
reader: add global reader instance counter
reader: consistent exit path for long running handler goroutine