feat: add option to emit semantic HTML for alerts

[flying-sheep]

fixes #821.

Design question: Maybe it should be made more generic, e.g. rename it to HtmlStyleType and have it affect tasklist_classes too – for some reason you don’t add a markdown- prefix for that class, only for alerts. But then it would be a breaking change as its default would either change render.tasklist_classes or extension.alerts.

[codspeed-hq]

Merging this PR will not alter performance

✅ 1 untouched benchmark

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_{Comparing flying-sheep:pa/alert-semantic-html (d2e4a46) with main (45c1995)}

[kivikakk]

Design question: Maybe it should be made more generic, e.g. rename it to HtmlStyleType and have it affect tasklist_classes too – for some reason you don’t add a markdown- prefix for that class, only for alerts. But then it would be a breaking change as its default would either change render.tasklist_classes or extension.alerts.

Maybe! The naming of the tasklist classes there was pretty arbitrary and decided upon by whoever implemented them at the time; I kind of think Comrak itself should probably not have much in the way of opinions about classes at all, and anyone who really wants them probably wants to implement a custom formatter.

But for now, we have what we have. (I'm pretty OK with breaking changes FWIW! What's the point of pre-1.0 if we can't have fun?)

Thanks so much for this PR! I really appreciate it. I'll add a CLI entrypoint and merge :)

[kivikakk]

This is part of Comrak v0.54.0!

[flying-sheep]

Thanks! This will help tools that support different markup languages!