lib/url.js: Add support for RFC 3490 separators

There is no need to split the host by hand in `url.js` – Punycode.js
takes care of it anyway. This not only simplifies the code, but also
adds support for RFC 3490 separators (i.e. not just U+002E, but U+3002,
U+FF0E, and U+FF61 as well).

Closes #6055.