This adds support for authentication data (`user:password`) in URLs,
IPv6 addresses, and unicode domains.

The test suite has been improved by adding test URLs from
http://mathiasbynens.be/demo/url-regex (with a few adjustments,
like allowing local and reserved IPs).

The previous URL validation regex failed this test suite on 13
occasions, the validator was updated based on
https://gist.github.com/dperini/729294.