Extract a list of links on webpage hosted at
Automatically resolves relative links relative to
body of the page will be automatically downloaded if not provided.
url must be an absolute URL starting with http:// or https://.
The links are returned as a vector of unique strings in arbitrary order.
Makes a best effort to extract links from malformed HTML and should not throw due to malformed HTML.
Due to the finniky nature of the web, this can only make a best effort, even if the HTML is well-formed. The exact huristics used are subject to change in a non-breaking release.