[x] Tweak the settings to approximate the default OSX icons as closely as possible (fix folder shade, mask shade, and bevel settings). (Fixed in 416d12ee4fa9e88802e7aff1454e9f34648b08d1 .)
[ ] Allow intermediate files to be generated and combined easily (e.g. to use a different source mask for the smaller icons).
[ ] Use -clone instead of writing to file.
[ ] Maybe: Handle automatic positive/negative detection, so that the mask doesn't have to be generated by hand.
[ ] Allow more procedural image generation (e.g. accept a string as input).