SleepDisplay 1.0

This is a utility that allows you to turn your Mac's display off or on. I wasn't able to find a way to do it without a 3rd-party utility, and this one seemed to be the most reliable.

In the original repo, the binary is CamelCased (`SleepDisplay`) – it's not very pretty, but I wasn't sure if it's ok to turn it into snake case?