func toUpper(ch rune) rune {
	if ch >= 'a' && ch <= 'z' {
		return ch - 32
	}
	return ch
}
toLower converts a character in the range of ASCII characters 'a' to 'z' to its lower
case counterpart. Other characters remain the same.
package strcase
func isLower(ch rune) bool {
	return ch >= 'a' && ch <= 'z'
}
func toLower(ch rune) rune {
	if ch >= 'A' && ch <= 'Z' {
		return ch + 32
	}
	return ch
}
func isUpper(ch rune) bool {
	return ch >= 'A' && ch <= 'Z'
}