events.go
func (e *EventLog) Errorf(format string, a ...interface{}) {
	Log.Printf("[ERROR] "+format, a...)
	e.el.Errorf(format, a...)
}
func (e *EventLog) Errorf(format string, a ...interface{}) {
	Log.Printf("[ERROR] "+format, a...)
	e.el.Errorf(format, a...)
}
// Errorf is like Printf, but it marks this event as an error.