Add URL constructor

[turbolent]

See https://url.spec.whatwg.org/#api and
https://developer.mozilla.org/en-US/docs/Web/API/URL/URL

[sjrd]

Given that the URL constructor does not seem to be supported in IE yet, this should go in the experimental package, in a file URL.scala. It's weird that the object URL and class URL won't live in the same package, but that reflects their respective level of support.

[sjrd]

That's all.

[turbolent]

Thanks for the feedback! Moved the class to the experimental package as suggested.

[sjrd]

There's a missing EOL at the end of the file here.

[sjrd]

Otherwise good for me. Could you squash your commits into a single commit, please?

[turbolent]

Squashed. You can also now do this straight from GitHub BTW: https://help.github.com/articles/about-pull-request-merge-squashing/

[sjrd]

LGTM.

GitHub does not let me squash your commits and create a merge commit for merging the PR, unfortunately.