Add session keep alive. If client doesn't send a keep alive, after a

specified amount of time the scheduler closes the session

event/event.go

@@ -15,6 +15,7 @@ var (
 	SESSION_END              = EventType("session end")
 	SESSION_READY            = EventType("session ready")
 	SESSION_BUILDER_OUT      = EventType("session builder out")
+	SESSION_KEEP_ALIVE       = EventType("session keep alive")
 )
 
 type Handler func(sessionId string, args ...interface{})