Setup some sort of autobuild + release packaging with GitHub

[xparq]

@azitmentor, your hands-on CI expertise may come in handy here.

-> README

[xparq]

Yeah, @azitmentor, creating a branch for it is a great idea! Could you please do it? (Basically to see if you have permission for that.)

[xparq]

@azitmentor Found this apparently "pure" nmake example at another project, perhaps we could use it:
https://github.com/zlib-ng/zlib-ng/actions/workflows/nmake.yml

Also, a nice guide: https://github.com/marketplace/actions/enable-developer-command-prompt

[azitmentor]

Nice guides, it was easy to start :-)

branch and build action done, please check the latest gha output for details

[xparq]

Thanks very much!

Now "the proper" method to add a lib as dependency (without including it in the repo), preferably without Docker, is what I need to figure out.

-> List of installed tools in the Windows runner images ...

(See also: https://github.com/marketplace/actions/github-action-build-chain-cross-repo-builds, https://stackoverflow.com/questions/61889035/how-do-i-use-github-actions-to-checkout-a-different-public-repo-then-add-some-f)

[xparq]

BTW, "release packaging" is still not done; splitting it into a separate issue (#19).