Simplify callback code with Nan callback helpers
Simplify callback code with Nan callback helpers

yfinkelstein/node-zookeeper,dfsxdev/node-zookeeper,dfsxdev/node-zookeeper,yfinkelstein/node-zookeeper,mdlavin/node-zookeeper,dfsxdev/node-zookeeper,yfinkelstein/node-zookeeper,dfsxdev/node-zookeeper,mdlavin/node-zookeeper,dfsxdev/node-zookeeper,mdlavin/node-zookeeper,yfinkelstein/node-zookeeper,mdlavin/node-zookeeper,mdlavin/node-zookeeper