R CMD Checks

[mhesselbarth]

In my experience, we make our lives easier and the code better if we avoid any Notes, Warnings, and Errors from the R CMD Check right from the beginning. So please make sure your pushes don't result in any issues and if so, try to fix them. This will probably happen quite a bit, at least for me :)

[Martin-Jung]

Fully agree. I tried to start with some basic tests, but haven't added Github actions yet.
We can make a general ruleset before making any PRs into dev:

• Add a test for any new function that was added.
• Run locally a full check and build the package.

[mhesselbarth]

Simple CI should be on dev due to #2