yaml front matter

[jerCarre]

could you support yfm support instead of comment syntax 👍

---
paginate: true
---

instead of

<!--
paginate: true
-->

yfm is supported in some MD editors (like typora)

[yhatt]

Already supported in Marpit, the base framework of Marp Next.
https://marpit.marp.app/directives?id=front-matter