slug.go
func IsSlug(text string) bool {
	if text == "" ||
		(MaxLength > 0 && len(text) > MaxLength) ||
		text[0] == '-' || text[0] == '_' ||
		text[len(text)-1] == '-' || text[len(text)-1] == '_' {
		return false
	}
	for _, c := range text {
		if (c < 'a' || c > 'z') && c != '-' && c != '_' && (c < '0' || c > '9') {
			return false
		}
	}
	return true
}
func IsSlug(text string) bool {
	if text == "" ||
		(MaxLength > 0 && len(text) > MaxLength) ||
		text[0] == '-' || text[0] == '_' ||
		text[len(text)-1] == '-' || text[len(text)-1] == '_' {
		return false
	}
	for _, c := range text {
		if (c < 'a' || c > 'z') && c != '-' && c != '_' && (c < '0' || c > '9') {
			return false
		}
	}
	return true
}
// IsSlug returns True if provided text does not contain white characters,
// punctuation, all letters are lower case and only from ASCII range.
// It could contain `-` and `_` but not at the beginning or end of the text.
// It should be in range of the MaxLength var if specified.
// All output from slug.Make(text) should pass this test.