io.go
func (da *Cedar) SaveToFile(fileName string, dataType string) error {
	file, err := os.OpenFile(fileName, os.O_CREATE|os.O_WRONLY, 0666)
	if err != nil {
		return err
	}
	defer file.Close()
	out := bufio.NewWriter(file)
	defer out.Flush()
	da.Save(out, dataType)
	return nil
}
func (da *Cedar) SaveToFile(fileName string, dataType string) error {
	file, err := os.OpenFile(fileName, os.O_CREATE|os.O_WRONLY, 0666)
	if err != nil {
		return err
	}
	defer file.Close()
	out := bufio.NewWriter(file)
	defer out.Flush()
	da.Save(out, dataType)
	return nil
}
// SaveToFile saves the cedar to a file,
// where dataType is either "json" or "gob".