Get the TLD from a FQDN.

Get the TLD part (eg.: com) from a FQDN (eg.: columbus.elmasy.com).

IMPORTANT: Only ICANN managed TLDs are returned, the private ones are only returned in the Top Level Domain. (eg.: columbus.elmasy.co.uk -> co.uk or columbus.elmasy.local -> local)

If Accept header is text/plain, returns the result as a string.