These `pub` here actually predate the pub(crate) feature, and theyshould just be `pub(crate)` or lower since they are unreachable outsidethe crate.

This is special for arrays of shape 1 x n or n x 1; add iterator anditerator sum (fold) benchmarks.

Implement axis merging - this preserves order of elements in theiteration but might simplify iteration. For example, in a contiguousmatrix, a shape like [3, 4] can be merged into [1, 12].Also allow arbitrary order optimization - we then try to iterate inmemory order by sorting all axes, currently.

This one complains about if let Some(_) = option; which I still think isjust as fine as if option.is_some(); `if let` is a nice Rust featurethat works the same way on all enums, no reason to preferoption-specific methods like `is_some`.