linkify

More strict parsing of hostname (authority) part of URLs. Applies to
emails, plain domains URLs (e.g. example.com/foo) and URLs with
schemes where a host is expected (e.g. https).

This fixes a few problems that have been reported over time, namely:

• https://www.example..com is no longer parsed as an URL (#41)
• [email protected] is no longer parsed as an email address (#29)
• https://*.example.org is no longer parsed as an URL (#38)

It's a tricky change and hopefully this solves some problems while
not introducing too many new ones. If anything unexpectedly changed
for you, please let us know!