Upgrade to latest numpy version which has good performance improvements
Add test for prune and scipy implementation of histogram.  Does not work with 16bpp images and scipy results are not compatible with ImageMagick results, on the todo list.
Scipy histogram implementation uses the core ImageLoading function.  A few other tweaks to return histograms just as ImageMagick version does.  More work needed
Added GetBitsPerPixel function
Add unique numpy memmap file names based on process and thread ID to assemble_tiles for use in cluster.  Still disabled by default.