Be able to fold/expand/contract text sections

I just wrote [a blog post with a fair amount of code](https://jensrantil.github.io/posts/simple-contract-testing/). I _think_ the article would be easier to read if the code could be folded and the reader could click on a header to expand/show the code. I could hack this using the tab feature, but it would feel...awkward. 😅 See this as a feature request.