func ReMap(pattern string, replacement string) PathMapper {
	re := regexp.MustCompile(pattern)
	return func(filePath string) string {
		if !re.MatchString(filePath) {
			return ""
		}
		return re.ReplaceAllString(filePath, replacement)
	}
}
func ReMap(pattern string, replacement string) PathMapper {
	re := regexp.MustCompile(pattern)
	return func(filePath string) string {
		if !re.MatchString(filePath) {
			return ""
		}
		return re.ReplaceAllString(filePath, replacement)
	}
}
// ReMap returns a PathMapper that compares file paths to the input pattern
// and maps matches to the replacement string (see Regexp.ReplaceAllString).