Setup now installs VC runtime if needed (issue #137) and some fixes/refactoring

On a newly installed Windows it's possible that the MS VC Runtime is not yet installed.
The setup now detects this and installs it for you if needed (issue #137).
Refer to the changelog for other changes.

Windows setup and binaries in assets.
Linux (Ubuntu 20.04 and up, Debian Bullseye and up) appimage in assets.