Support subscribe a channel

[shwangdev]

Current version can not subscribe a channel.

If this client can support this feature , it would be the best client for redis.

[drjtan]

need it badly: how to read messages after "subscribe"???!!!

[kevinkjt2000]

@wxjeacen @drjtan I am thinking about implementing this. How does adding a parameter to subscribe and psubscribe that allows a function callback? (i.e. a function pointer)