Emit follower event on first join

[connor4312]

When a raft first joins the cluster as a follower, and event does not appear to be emitted. This is my ugly fix for that...

    raft.on('follower',      function () { self.emit('follower'); });
    raft.on('leader change', function () {
        if (!self._emittedFollower) {
            self.emit('follower');
            self._emittedFollower = true;
        }
    });

[3rd-Eden]

Hmm, yea, that needs fixing. Making as a bug.

[connor4312]

Perhaps a better way would be to have a "DISCONNECTED" state to represent a raft that's not joined a cluster yet, or has dropped out of the cluster (e.g. a local network failure). That would add some additional useful info and, as a side effect, emit the first follower event.