Canonicalised format, made readable, used more standart functions.

The theme itself looks interesting to me. I had some sketches about how it can work in the past.

I re-formatted the code as it is recommended and as I do (so I was able to read and understand).

I also remade all equation-style functions into a `case ... of` ones for simplifying future refactoring.

I made `applyAt` traverse the list once.

Other small changes: `intercalate "\n"` == `unlines`, the `loadBoardFromText` inner `loadBoard` became a `foldl`, some expressions turned into `zip as bs 'for' \(a, b) -> c` where `for = flip map`.

I didn't touch main domain algorithms, it hard to reason what is/should be done there.

The code looked as you used the tab button. Tab is a no-no, please, don't use it.