Adds IsReconnecting and Status methods on Conn

This adds two methods onto nats.Conn to return the current state of the
connection (the nats.Status type), and a method to check if the client is
reconnecting. This is mostly for parity with the IsClosed method.
Add tests around IsReconnecting and Status helpers
Merge pull request #27 from apcera/add-conn-state-methods

Adds IsReconnecting and Status methods on Conn