Port the every command

[pantonshire]

I wasn't completely sure how to handle negative strides; I'm silently casting them to usize because this is what the nth command does, but perhaps returning an error would be more appropriate?

[sophiajt]

It's probably good for now - we'll probably circle back later and keep improving the errors as we go.

@pantonshire - if you want, you could file an issue so we remember to go back and improve the error later