TODO
- http://primercss.io/colors/
- https://allejo.io/blog/a-jekyll-toc-in-liquid-only/
- https://github.com/github/pages-gem#bypassing-the-plugin-whitelist
- Add anchor icons, https://www.bryanbraun.com/anchorjs/#examples.
- Use Sass for Bootstrap and GitHub rather than CSS alone (so as to have access to variables).