Add image processing algorithms to OpenImageIO

by Stefan for OpenImageIO

I propose many image processing algorithms to be added to OpenImageIO. I have already implemented, tested and documented the algorithms, but many modifications are needed before they are accepted. The main categories are histograms, point operations, filters, edges, corners, lines and morphological operations. The modifications needed are working with image regions, using more threads, working with images with arbitrary number of channels, using arbitrary pixel data values, working in 3D, etc.