Remove unnecessary allocations

[cospectrum]

The only public change: convex_hull.

[theotherphil]

Thanks for the PR. Does replacing a nested loop with Image::from_fn have any impact on the image filtering benchmarks?

[cospectrum]

Image::from_fn iterates in the same order (row-major, cache friendly), so it should be the same. Plus, you don't have to think about the row-major vs col-major every time.

[cospectrum]

Image::from_fn iterates in the same order (row-major, cache friendly), so it should be the same. Plus, you don't have to think about the row-major vs col-major every time.

Hmm, not really. A small regression. It seems that the compiler cannot optimize the mutable lambda

[cospectrum]

Or the iterators are to blame.

[cospectrum]

A couple of minutes. I'll refactor incrementally

[cospectrum]

@theotherphil, Now I think my bilateral_filter bench is better than the master (both allocs and speed).

[theotherphil]

Great, thanks!