New notification system added that can be used by scripts or programs that want to send notifications through Fenrir. Separate from self-voicing.

internal/command/command.go

@@ -24,6 +24,8 @@ type ID string
 const (
 	Time                  ID = "time"
 	Date                  ID = "date"
+	LastNotification      ID = "last_notification"
+	NotificationHistory   ID = "notification_history"
 	PreviousLine          ID = "previous_line"
 	CurrentLine           ID = "current_line"
 	NextLine              ID = "next_line"