Avoid using stride when clipping

[gabrieldansereau]

clip currently uses the stride, which might return approximation errors as in #144.

@tpoisot had an idea to avoid using stride completely. Possibly using indices instead of coordinates?

[tpoisot]

I'm going to take a look at where we use stride internally, because I think we would get rid of so much edge cases by using indexing directly. I'll open a PR when I'm done.