Integrates Github Actions which is much much faster than AppVeyor in all areas, and even supports multiple workflows instead of forcing everything into just one workflow like AppVeyor does. Plus we get 20 parallel builds that nearly instantly finish, which results in much faster feedback without having to run our own Jenkins CI.
The builder and packager scripts have been adjusted to add support for both Windows and Linux, and both AppVeyor and Github Actions. Additionally to that, the builder script now correctly executes x32 and x64 steps in a chain, instead of waiting for the other architecture to finish first. This further reduces build times.
Massively speeds up repeated builds by not relying on random undeterministic download speeds of the AppVeyor machines, in addition to reducing the stress on the remote end for each build done. Additionally the logging changes make it so that the errors and warnings are shown in the AppVeyor UI.