support protocol version

[caserzer]

@takanorig thanks for the great work, it would be nice including:

1. Support protocol version , by default it's use old protocol version , you can add option for version 3.1.1
2. Async create the connection, we run huge load test , we need create 100K connection on one load agent, sync connect is too slow.
3. I'm go newbie , async close connection cause server side report client forcedly close connection, but when I modify the code to sync close, it run correctly.