log/logger.go
func (l *Logger) Debugf(format string, args ...interface{}) {
	l.Output(2, LevelDebug, fmt.Sprintf(format, args...))
}
func (l *Logger) Debugf(format string, args ...interface{}) {
	l.Output(2, LevelDebug, fmt.Sprintf(format, args...))
}
// Debugf records the log with debug level