[initial commit of averaging tools raph.levien@gmail.com**20060417213225] [do two-pass blending with outlier culling raph.levien@gmail.com**20060418003148] [normalize, sharpen and gamma correct blend images raph.levien@gmail.com**20060418010723] [minor fixes (pnm compat) raph.levien@gmail.com**20070418141404]