Move to external userspace

[burkfers]

A demo of the concept ("it compiles" only, no documentation changes) is available here: Base repo: https://github.com/finrod09/qmk_firmware/tree/bkb-master-userspacebase Userspace: https://github.com/finrod09/qmk_userspace/tree/bkb-userspace

Todos, should we want to move forward with this:

• [ ] Upstream all outstanding keyboard changes, specifically the flattening/legacy removal
• [ ] Remove via keymaps from upstream
• [ ] Remove via keymaps from here
• [x] Create bkb-userspace reposistory with the correct ownership
• [x] Create GitHub action in userspace repository that checks out and compiles against bastardkb-qmk
• [ ] Document
  • [ ] Extend the board readmes to point at the userspace to access "real" keymaps (not default)
  • [ ] Document userspace setup/compilation process in the top level userspace readme

Wishlist:

• [ ] selectable base alpha layout for all boards
• [ ] break out shared code into a reusable library (requires discussion)

[bstiq]

Once this is done,

• [ ] update the docs: https://bstiq.github.io/bstiqbstkbd.github.io/fw/compile-firmware.html