Allow underscore and tilde in URI hostnames as per RFC 3986

[longwave]

The implementation of RFC 3986 in the URI validator is more strict than the specification allows. While the RFC says

URI producers should use names that conform to the DNS syntax, even when use of DNS is not immediately apparent

the host component grammar actually allows more characters than are allowed in DNS names.

This is a problem for the Drupal project which uses this package in conjunction with custom stream wrappers with module names in the host component. Module names conform to PHP function name standards, not DNS standards - that is, they allow underscores but not dashes.

The relevant RFC grammar is

      host        = IP-literal / IPv4address / reg-name

      reg-name    = *( unreserved / pct-encoded / sub-delims )

      unreserved  = ALPHA / DIGIT / "-" / "." / "_" / "~"

This PR widens the host validation to allow all characters in the unreserved set. While pct-encoded and sub-delims are also technically allowed, this is the smallest change that will help us out.

[DannyvdSluijs]

Thanks for the PR, nice work. I've left one small suggestion on the test to also include a test case for the tilde character.
Could you also add an entry in the CHANGELOG.md ? This way I can merge the PR without adjustments with saves me some time.

Once done it should be easy to create a new release and the issue in your project(s) should be resolved.

[DannyvdSluijs]

Version 6.6.2 was released, see https://github.com/jsonrainbow/json-schema/releases/tag/6.6.2

[longwave]

Thank you for the super fast response!

[wimleers]

WOW! Incredible!