I had some fun and implemented somewhat different version of how code is
fetched, and buttonized toggle function.

Since I really didn't got much more input than what Martin gave me yesterday, I
have had some fun and recorded a small demo of how it looks like:

https://youtu.be/yiS1eXdgcYI

Sorry, but I don't have better place to put it on, use yt-download if you prefer
not to open it in a web browser. It is just a two minute of me showing how it
looks when used in practice. I reason that looking at the code is one thing,
seeing it is the other.

I have also changed it a bit, and pasting the source after the navigation
buttons. so they don't jump out of the screen when a function is very big. Don't
know if it is better strategy, it is just a prototype anyway.