Pandoc: Resolve relative URLs in Markdown input

[larsgw]

Some Markdown URLs are relative, e.g. these image URLs of https://github.com/egonw/blog2/blob/new/_posts/2025-01-04-isaac-browser-extension.markdown?plain=1:

To use the extension, the user would take the following steps.
First, click the “Toevoegen” button, green-blue with white letters in the above
screenshot. This would give a page like this:

![](/assets/images/isaac2025_2.png)

These should be able to be resolved against the URL of the page. Ideally this is also done for normal <a> links, not just images.

This could be done with a Lua filter: jgm/pandoc#4894

[larsgw]

(now, the images are not included in the generated PDF as a result)