Initial Python version. Too slow.
More Python work.
Option for revealing target in Finder.
Display the number of cores available in the help desciption for --num-workers.
Fix pre-Yosemite code. Fixes #17.
Fix bug when using target.

The (temporary) iconset folder wasn't getting created.
Change target to a positional argument.
Rename mask_file to mask.
Change OSX version to optional flag instead of choice.

If the folder changes again in a future version, we'll figure something out.
Remove test.icns and test.iconset.