Advent of Nim 2020 megathread

[martinc]

Here's my code: <https://github.com/martin-c/aoc2020-nim>. I'm new to Nim and 
started late, so it may not be a great resource. I did create a way to 
automatically save the input filename from a URL using `os.execShellCmd` and 
`wget` so there's that in case anyone is interested. I exported my cookie(s) 
for <https://adventofcode.com>/ from firefox using the Export Cookies addon.