code: func NewLogger() *Logger {
  	logger := &coreLogger{
  		ErrorWriter: os.Stderr,
  		BufferSize:  1024,
  		MaxLevel:    LevelDebug,
  		Targets:     make([]Target, 0),
  	}
  	return &Logger{logger, "app", DefaultFormatter}
  }
docs: // NewLogger creates a root logger.
  // The new logger takes these default options:
  // ErrorWriter: os.Stderr, BufferSize: 1024, MaxLevel: LevelDebug,
  // Category: app, Formatter: DefaultFormatter