code: func NewFileTarget() *FileTarget {
  	return &FileTarget{
  		Filter:      &Filter{MaxLevel: LevelDebug},
  		Rotate:      true,
  		BackupCount: 10,
  		MaxBytes:    1 << 20, // 1MB
  		close:       make(chan bool, 0),
  	}
  }
docs: // NewFileTarget creates a FileTarget.
  // The new FileTarget takes these default options:
  // MaxLevel: LevelDebug, Rotate: true, BackupCount: 10, MaxBytes: 1 << 20
  // You must specify the FileName field.