Add a shortcode for the image compare slider

[nicopap]

This streamlines the process of creating image comparisons.

The downside is that macro invocations in zola do not admit trailing commas in argument position, so it is error prone.

[ickk]

A little bit of bikeshedding: I feel like maybe "left"/"right" might be better names than "before"/"after". For example, in the case of a comparison between msaa & taa "before"/"after" doesn't necessarily fit semantically.

[nicopap]

Looks like building the site breaks when using the page.colocated_path parameter to evaluate the image's aspect ratio.

This seems to be an error with the version of Zola we use (0.16.1 if I'm not mistaken) there are mentions of fix for colocated_path in the Zola changelog of more recent versions: https://github.com/getzola/zola/blob/master/CHANGELOG.md#0172-2023-03-19

[BD103]

Zola has finally been updated to 0.18 (per #1018, thanks Trial!). Does this PR need any other work to get merged?

[nicopap]

I'll check it out in the following days and open if it's ready.

[SIGSTACKFAULT]

Adopting :)

[ickk]

closing in favor of #1144