A simple Python script for launching Minecraft. You could use it as a template to make custom Minecraft launchers for modpacks and stuff. You might find it useful, idk. Do what you want. It's on the BSD license FYI. So yeah. Not much to be explained.
They are in the mcdata folder that this scripts creates instead of the normal .minecraft folder.
Well, yeah, obviously. Except when you're installing Forge, you must direct it to the mcdata folder instead of the default .minecraft folder unless you made a shortcut/symlink there or something.