Relative entry links are broken

Steps to reproduce

• Use the RSS macro on a feed whose entries have relative links, for example an Atom entry with <link href="/posts/1"/>.

Expected

The entry title links to the entry on the site hosting the feed (e.g. https://example.org/posts/1).

Actual

The link is output as is (href="/posts/1"), so the browser resolves it against the wiki page and the link is broken.