init add writer

allow custom heartbeat interval setting when call NewWriter()
auto send IDENTIFY when call ConnectToNSQ()
write message via Publish()/MultiPublish()
Merge pull request #164 from datastream/master

go-nsq: add Writer API
Added table headers to channel table for disambiguation of gauges and counters
Merge pull request #184 from elubow/master

nsqadmin: Disambiguating Table Headings in Channels
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