Make documentation compatible with Docusaurus

Is your feature request related to a problem? Please describe.
Docusaurus uses Markdown documentation with minor differences from mkdocs.

Describe the solution you'd like
Add Yaml front-matter. Move title from h1 header to front-matter title field. Add sidebars.js.

Describe alternatives you've considered
I considered run-time conversion but this does not appear to be worth the effort right now.