Markdown support

[Matistjati]

supported for both pdf and html:

• problem name and id are automatically inserted at the top of the statement. Spec that we automatically prepend it from problem.yaml
• samples
• interactive samples
• {{nextsample}} and {{remainingsamples}}
• commonmark-style images
• "common" footnotes. extended commonmark syntax
• "common" tables. extended commonmark syntax
• inline and display math with $a+b$ and $$a+b$$

A PR of the spec can be found here Kattis/problem-package-format#386.

todo in follow-up pr:

• svgs, both for md and html. need to be sanitized
• better CSS class names for Kattis
• CSS styling closer to Kattis

not planned to be added in this PR (maybe ever):

• tex -> html using pandoc (remove plastex)
• tex -> pdf using pandoc (we will keep using pdflatex for this)
• pdf images (they look terrible)
• webp images (poor support)

[gkreitz]

I took another pass over it, as requested. This is getting close to ready for merging. The main problem I see are a couple of places where we need to escape latex characters (the rendering path of markdown -> latex -> pdf that pandoc does is funky...).

[gkreitz]

Looks good, code just had two small things. Tests failing due to UUID should be fixed by #307 merging (and then rebasing on that).

For example problems, I'm ok with merging this as-is, but if so we should do a follow-up soon where we convert the problems to 2023-07.

[gkreitz]

guess is a legacy problem, which does/should not support markdown. I'd like for our examples to follow the standard.

One way to fix that would be to convert guess and/or oddecho (where you also added a markdown statement) to 2023-07-draft.