Switch to Docusaurus?

[inteon]

https://docusaurus.io/ looks like a very mature and capable framework.
In hindsight, it is a bit strange that this repo does not use such a framework.
Features of that framework:

• tabs (https://docusaurus.io/docs/next/markdown-features/tabs)
• versions (https://docusaurus.io/docs/next/versioning)
• better codeblocks (https://docusaurus.io/docs/next/markdown-features/code-blocks)
• ...

This would allow us to replace a lot of our custom code with tools from docusaurus.
This repo would just contain all the content for the website and a theme for docusaurus.