I was surprised to learn that this package didn't support [URL](https://developer.mozilla.org/en-US/docs/Web/API/URL) types, especially as they have a [`toJSON`](https://developer.mozilla.org/en-US/docs/Web/API/URL/toJSON) method natively. `Date` and `RegExp` types are supported, so I figured URLs were a pretty clear case. Is this something that can be added?