#7 Add rainbow delimiters

https://www.emacswiki.org/emacs/RainbowDelimiters

I haven't used it yet, but I keep meaning to try it out. And even if not using this package, I suspect that distinguishing braces will help in the same way that alternating and cycling through them helps when writing a proof on the chalkboard.

Or perhaps use ParEdit.

https://www.emacswiki.org/emacs/ParEdit

Adding paredit. Not using rainbow-delimiters because too subtle out of the box and/or my color settings seems to affect it negatively.