Add github workflow

[ufechner7]

While you have unit tests, they are not executed when creating or merging a pull request. Please add a workflow that:

• runs the unit tests
• checks the code coverage of the unit tests
• builds the documentation
  preferably on Windows, Mac and Linux, but if its easier to make it work on one OS than start with that first.

[Clemapfel]

I already cleaned up the build scripts so they now work on everything without restriction, the jll should be live in the next week,
after which I can immediately register mousetrap with the Julia registry.

Once that's merged, installation is just add Mousetrap and CI should be fairly easy then. It is definitely planned next, thank you.