Add release workflow

[sermuns]

This adds a GitHub action workflow that compiles the program for MacOS, Windows and various architectures of Linux.

I did a little tinkering with the git history to make the commits make the most sense, by adding the workflow before version 1.0.1. Let me know if this is stupid.

I also replaced = with # in CHANGELOG.md, let me know if there was a reason for this otherwise.