New SuperColliderAU repo

Hey all,

As agreed upon in previous discussions, I've set up a new organization repo
for SuperColliderAU and given Gerard Roma push access, since he has
expressed interest in maintaining it.

https://github.com/supercollider/SuperColliderAU

This means that we should soon merge PR #3540 which removes the project
from the main repo, once the code is up there. I will also work with him to
add CI so that breaking changes can be caught early.

One thing is still unclear to me - does this need to be a submodule within
SC proper, or can it exist as a separate project that builds using SC libs,
similar to sc3-plugins?

Thanks again to Gerard for reviving this project!

Regards,
Brian