Allow punycode emails

[fraserredmond]

An example from the comments on https://isemail.info

почта@домен.рф turns to [email protected]

Both of those emails fail. Seems like it's the xn-- and @- that cause it to fail. As a workaround I'm replacing them to "xn" and "@" before passing to is_email.

[Lockhead]

You should change the title, as this example E-Mail also needs SMTPUTF8 compatibility, punycode only covers the domain-part of an email. So you can't puny encode the local-part...