Handle relative links

[mre]

WIP for #1296 and #1480

This just adds a failing test based on @nobkd's minimal repro.
I didn't fix the underlying issue.

[mre]

It doesn't run the failing test yet. See #1483.
The Docker build failure is unrelated.

[nobkd]

Might also be interesting/relevant. Not sure if this is maybe already used by lychee. 🤷‍♂️
https://developer.mozilla.org/en-US/docs/Web/HTML/Element/base

[mre]

Might also be interesting/relevant. Not sure if this is maybe already used by lychee. 🤷‍♂️
https://developer.mozilla.org/en-US/docs/Web/HTML/Element/base

Very interesting; I never heard of it.
The current implementation is pretty basic, and we don't use <base>. Looking at the docs, there seem to be quite a few different cases to be handled, so I'd like to postpone handling that for now. But thanks for the tip.

[mre]

Superseded by #1489.