Get the GitHub Actions to be run by Windows and macOS runners as well as Linux.

[drwhut]

This way, we can test Decision continuously on all 3 platforms: Windows, macOS, and Linux.

[drwhut]

Look here for an example.

[drwhut]

The script files used for testing will not work for Windows, so try and use CMake to test instead?

If so, then add to README.md how to test from the command line: ctest -C Debug.