Switch to XDM

[with-heart]

https://github.com/wooorm/xdm

This would give us lots of benefits like hot reloading, automatic loading of pages/**/*.mdx files, and a number of cool features listed in the project's README.

[with-heart]

I made a good amount of progress on this but I really need to figure out how to access frontmatter, either from within an mdx file or from components.wrapper or something. I tried the recommended instructions but if remark-frontmatter and remark-mdx-frontmatter are working, I can't access {frontmatter.title} or {title}.

Would be nice to understand how to debug this problem too.