modular no-temp swap

[Rudxain]

This uses destructuring syntax, to avoid the potential confusion of temporary vars. It also defines a swap fn that mutates whatever array is passed as input, without returning it.

A more functional approach would be to shallow-copy the array, mutate the copy, then return it. Should we do that instead?

BTW, let temp can be replaced by const temp (#3 closes it)

[Rudxain]

Nvm, I think it's better to keep the code as-is, for better variety. I've seen other files already using destructuring syntax, and other files using the modular-temp approach