Jekyll 4

[TWiStErRob]

• Prerequisite Work through Jekyll 3 TODOs #34
• Prerequisite Use GitHub Actions deployment for GitHub Pages #24
• Feature request: Support for Jekyll 4.0 github/pages-gem#651
• Infeasibility explainer: Support for Jekyll 4.0 github/pages-gem#651 (comment)

Motivations:

• Jekyll serve fails on Ruby 3.0 (webrick missing) github/pages-gem#752

Workarounds:

• 2019: move to Netlify or other third party.
• 2019: https://github.com/BryanSchuetz/jekyll-deploy-gh-pages (hacky push to gh-pages branch)
• 2020: Deployment from a branch
• 2022: Official response, GitHub Pages custom actions workflows.
• Official 2022 solution implemented in Deploy to GitHub Pages with custom workflow #25

Tasks

• https://jekyllrb.com/docs/upgrading/3-to-4/

[TWiStErRob]

• Solves Excerpt: Footnote definition <...> is unreferenced - ignoring jekyll/jekyll#7576

     Generating...
  Kramdown warning: Footnote definition for '1' on line 3 is unreferenced - ignoring
  Kramdown warning: Footnote definition for '2' on line 4 is unreferenced - ignoring
  Kramdown warning: Footnote definition for '3' on line 5 is unreferenced - ignoring
  Kramdown warning: Footnote definition for '4' on line 6 is unreferenced - ignoring
  Kramdown warning: Footnote definition for '5' on line 7 is unreferenced - ignoring
  Kramdown warning: Footnote definition for '1' on line 6 is unreferenced - ignoring
  Kramdown warning: Footnote definition for '1' on line 7 is unreferenced - ignoring
  Kramdown warning: Footnote definition for '1' on line 5 is unreferenced - ignoring
                    done in 10.164 seconds.

[TWiStErRob]

Review Ruby Sass usage after upgrade: #31 (comment), note https://jekyllrb.com/news/2022/12/21/jekyll-sass-converter-3.0-released/

[TWiStErRob]

Review setup guide in README.md, extract to DEVELOPMENT.md