drop RDY count on existing connections

* fix a bug in how amount of allowed RDY to send was calculated
Merge pull request #258 from jehiah/new_connections_rdy_258

reader: update RDY on existing connections
Merge pull request #259 from mreiferson/persist_race_259

nsqd: race when persisting metadata
writer: refactoring to support async functionality
nsq_to_nsq: proxy a topic from producer(s) to destination nsqd over TCP
fixes
fix build
cleanup
consistent heartbeat logging
better heartbeat message
add reconnect crap