Added support for Bitfinex Websocket heartbeat.
Added support for Bitfinex Websocket heartbeat.

jmaurice/gocryptotrader,snipesjr/gocryptotrader,thrasher-/gocryptotrader,thrasher-/gocryptotrader,snipesjr/gocryptotrader,thrasher-/gocryptotrader,thrasher-/gocryptotrader,snipesjr/gocryptotrader,thrasher-/gocryptotrader,snipesjr/gocryptotrader