Add IPv4 addresses support to lib\HostProcessing::parseHost(), lib\HostProcessing::serializeHost(), URL::domainToASCII() and URL::domainToUnicode().
To reflect whatwg@9043740.

This commit broke backwards compatibility.
Because it modified lib\HostProcessing::parseHost() to return an integer or float in case of IPv4 address, and lib\URL::host to have one in the case.