* Move all markdown into a dedicated `content/` directory
* use contentlayer (https://github.com/contentlayerdev/contentlayer) for loading markdown
* add catch all route pages/[...slug].js to generate all markdown routes using contentlayer to find pages
frontmatter now properly supported
NB: some nice side benefits like removing the hack in _app.js to render markdown template vs the general layout template
TODO: page titles need fixing
Note this works by getting the page path (slug) and unparsing it e.g. '/claims' => Claims. 'notes-on-neometallism' => 'Notes on neometallism'.
In future, we may have title explicitly set in the front matter (or otherwise) and we can use that.