Add endpoints for specifications needing to parse URLs

This makes the following changes:

* It renames parse a URL to encoding-parse a URL, signifying it takes into account the encoding of the document or environment.
* Similarly it renames parse and serialize a URL to encoding-parse-and-serialize a URL.
* It adds parse a URL that does not take into account the encoding of the document or environment.
* It exports both parse a URL and encoding-parse a URL and adds some guidance for specification authors.