Implement a remark plugin to embed typst in markdown documents

[quank123wip]

Since several markdown renders supports using MathJax or KaTeX to render math contents, it's a good idea to make typst an alternative option.

And, of course, markdown-it is a good option too, but I'm not going to work on it.😮‍💨

I'm going to work on this months later, just regard this issue as a reminder here. Of course, volunteers are welcomed.