[FEATURE] Raise a Punchblock::Connection::Disconnected event

Up to now we can listen for Punchblock::Connection::Connected events, but I needed to know when Punchblock loses connection to the FS Event Socket. I added that event in a similar fashion as Connected event works.

PS: Again, I screwed up the branch and we should close the other pull-request: https://github.com/adhearsion/punchblock/pull/176 sorry! :)