Ex. 100 shall be the new multi-object for loops

[ratfactor]

I'm really excited about this new language feature because I discovered it right at the very moment when I needed it (comparing two arrays, in my case):

ziglang/zig#14671 (PR)

ziglang/zig#7257 (initial proposal)

This is something that has always annoyed me about languages with iterators - you can iterate one thing, but if you want to iterate over a second thing as well, you have to use indexing and an index variable like a stone-age cave person!

Anyway, I'm creating this issue to reserve the Exercise 100 spot. :-)