log.go
func (l *slog) Debugf(format string, args ...interface{}) {
	lvl := l.Level()
	if lvl <= LevelDebug {
		l.b.printf("DBG", l.tag, format, args...)
	}
}
func (l *slog) Debugf(format string, args ...interface{}) {
	lvl := l.Level()
	if lvl <= LevelDebug {
		l.b.printf("DBG", l.tag, format, args...)
	}
}
// Debugf formats message according to format specifier, prepends the prefix as
// necessary, and writes to log with LevelDebug.
//
// This is part of the Logger interface implementation.