Finish build script overhaul

• Drop support from the build script for clean builds and capturing logs as these don't work well when running multiple builds in sequence.

• Don't copy deployed files to the pub directory in the build script - artifacts will land in the new output directory used by the oryx-image recipe instead. The output directory is configurable via the -o/--output-dir argument and defaults to build/images.

• Support building for multiple machines in the build script. The --all-machines argument can be passed to support building for every supported machine. If no machines are listed then bitbake is not ran (this is useful for building just the docs).

• We don't need to set TOPDIR in the build script as bitbake automatically sets this.

• Additional build script arguments --rm-work, --dl-dir, --sstate-dir are supported with obvious meanings.

• The new build script argument --source-archive creates a full archive of the Oryx sources (bitbake, layers, build scripts & config). This relies on git-archive-all being installed. This will be used by release builds.

• The new build script argument --checksum creates checksums of all artifacts placed in the output directory. This will be used by release builds.

• The new build script argument --docs builds the documentation.

• The old ci/run.py script and ci/auto.conf config file are dropped as the build script now handles everything we need for CI.

• CI is updated to use the new build script arguments and is re-arranged into three jobs: native-images, guest-images and docs. Each of the images jobs builds for all supported machines.

• meta-oryx is updated to bring in changes from meta-oryx!32 (merged).

• COPYING and README.md are updated.