Consider supporting MDX

[CraigCav]

This would provide us an alternative to needing to provide "scope" in our examples, and would be a better fit for documentation tools like docx.

We should consider how we can "discover" examples from mdx files, in particular, it's unlikely we want to generate snapshots of the playground component from docx (for example). Perhaps we can provide a "Sosia" component that could be put inside the playground, that is otherwise inert?