Fix typo in macOS step.

Replace ZIP action with installing p7zip.

For MacOS, remove ZIP action which was restricted to linux containers,
and add installation of a 7zip port - p7zip instead.

Re-enable full build matrix.

Fix artifact target folder creation for macOS.

Adjust macOS archiving steps. Disable nix and win.

Fix delimiters, disable artifact upload on macOS.

Fix context variables. Temporarily disable macOS.

Add toolchain update (and installation on macOS)

Fix artifact name and add note about double-zip.

Add release Github Workflow.

Add workflow for pushed tags which start with "v", and update README
accordingly.
Add note about rust not being available on macOS runners.