Advent of Nim 2020 megathread

[fxn]

Did that anyway, feels cleaner. The top-level code does
    
    
    toSeq(stdin.lines).map(parseInstruction)
    
    
    Run

This is the [iterated solution for part 2 (day 
8)](https://gist.github.com/fxn/bbd90877bcd27581ee5f7720495c3c3f). Anything 
else to improve please just tell me!