Add support for safe html tags in custom markdown

[lovasoa]

Discussed in https://github.com/sqlpage/SQLPage/discussions/729

^{Originally posted by beingalink December 9, 2024} Hi all,

I'm just trying to use markdown columns for being able to display superscript (i.e. 1.345^p,q). Unfortunately, I can't figure it out as neither ^p,q^ nor <sup>p,q</sup> seem to work. Am I missing something? Thanks for your help in advance!

Ideally we would support the entire GFM (Github Flavored Markdown) and could reference existing documentation for it https://github.github.com/gfm/