open alarm and netconf notifications client

[beckyxu]

I use CREATE_SUBSCRIPTION to enable server send notifications to client.But it seems
official don't have a common method or example to use .Can
official write one?

[nemith]

Currently notifications aren't support and adding them into the current version would be difficult due to the sync nature of the messages. However I am working on a complete v2 rewrite which supports interleaved messages for notifications. No ETA

Follow the progress on (#24)