It is necessary to skip to 4.2, because 3.9 (in Debian) does not
support Ruby 3.0.
Also, remove GitHub Pages stuff and add some gems to make it all work.
* Use a newer Jekyll version and also use bundler
* Use the `jekyl-theme-hydeout` theme gem
* Add support for Jekyll Admin (if you want to use that)
* Transform the index news items to posts
* Use Markdown instead of Textile for the pages