Slides: Add "markdowny" way for vertical slides

Use case or problem

When doing a quick slide presentation using Obsidian, there is no easy way to use vertical slides.

Using <section> somehow helps, but is clunky and doesn’t interpret Markdown.

It seems data-separator-vertical isn’t defined in the embedded reveal.js.

Proposed solution

Would it be possible to define a “markdowny” vertical slide separator? Maybe *** or +++ or even ---- or the like?

So we could use slides like …

## Slide 2


## Slide 2.1


## Slide 2.2


## Slide 3

where “Slide 2.1” and “Slide 2.2” are vertical slides below “Slide 2” and “Slide 3” is the next horizontal slide?

I think *** should be preferred over +++, since it also produces a <hr> when used in normal preview.

Current workaround (optional)

None that really functions.

Related feature requests (optional)