Important project changes, both technical and not.

Highlights:

- important (non-technical) project changes

- hundreds of kernel and user space related bug fixes

- added rolling Debian (sid) based releases

- added generic stable and rolling UEFI arm64 & x86 images

- added Raspberry Pi images

- upcoming Ubuntu 22.04 LTS images are ready

- new Extensions build framework

- extensive build automation (CI/CD) improvements

Armbian is a Debian-based distribution for Arm-based single-board computers (SBCs).