treewide: Change URLs to HTTPS

Lots of URLs were HTTP redirect to HTTPS. Changed those and checked them
if there's actual content. Inspired by
https://github.com/NixOS/nixpkgs/issues/60004

doc/languages-frameworks/vim.section.md

@@ -250,6 +250,6 @@ override to the `pkgs/misc/vim-plugins/default.nix` in the same directory.
 - [vim-pi](https://bitbucket.org/vimcommunity/vim-pi) is a plugin repository
   from VAM plugin manager meant to be used by others as well used by
 
-- [vim2nix](http://github.com/MarcWeber/vim-addon-vim2nix) which generates the
+- [vim2nix](https://github.com/MarcWeber/vim-addon-vim2nix) which generates the
   .nix code