Composable generic way to achieve n-ary zips of arrays

[bluss]

Just brainstorming

A "builder pattern" approach may be viable here to allow n-ary zipping operations. We could even allow masking (?) which is a very valuable operation.

zip_mut(&mut a).zip(&b).zip_mut(&mut c).apply(|x, y, z| *x = *y + *z);

// This is intended to do the same as this would in numpy
// mask = c > d;
// a[mask] = b[mask]
zip_mut(&mut a).zip(&b).mask(&c, &d, <_>::gt).apply(|aelt, belt| *aelt = *belt);

[bluss]

Close in favour of #231