log_adapter.go
func (la *LogAdapter) Warningf(msg string, a ...interface{}) error {
	return la.Log(LevelWarning, nil, msg, a...)
}
func (la *LogAdapter) Warningf(msg string, a ...interface{}) error {
	return la.Log(LevelWarning, nil, msg, a...)
}
/*
Warningf uses msg as a format string with subsequent parameters as values and logs
the resulting message to all added loggers at LogLevel.LevelWarning
*/