part of the image wasn't just zero padding along the border.

allow you to adjust the width and height independently.

of spatially_filter_image_separable() that does downsampling at the same time
as it does the filtering.

doesn't need to be the same size on all sides of a rectangle.

results to an output image rather than overwrite the contents
of the output image.

normalization constant was being computed incorrectly.

a new function called sum_filter().

calling get_best_matching_rect().

reconstruct them for each separation oracle call.

Also improved its spec.