ToASCII converts a domain or domain label to its ASCII form. For example,
ToASCII("bücher.example.com") is "xn--bcher-kva.example.com", and
ToASCII("golang") is "golang".
ToUnicode converts a domain or domain label to its Unicode form. For example,
ToUnicode("xn--bcher-kva.example.com") is "bücher.example.com", and
ToUnicode("golang") is "golang".