Create a CLI

[knothed]

Currently, gnimag is executed by adapting the code in the main.swift file (i.e. selecting your game and changing input/output/debug options) and then running gnimag from Xcode.

We ultimately want a CLI to allow running gnimag from the command line. This could look like this:

gnimag run mrflap
gnimag run mrflap -in scrcpy -out simple-arduino
gnimag run mrflap -debug ~/Debug
gnimag help
etc.