CI/CD with Bitrise

To make the development process more reliable, I added 4 of the open-source libraries on my GitHub account to Bitrise. For small developers they offer a free service to have automated build pipelines for different platforms, including the Apple ecosystem.

Every commit will now trigger the build pipeline including running the test set (if present, which is currently not the case for part of my code). At least it will trigger in case existing builds fail. The build status will also be presented on the repository page.

There were some dependencies in 2 of the libraries on UIKit, which were causing build issues. The easiest way to solve that turned out to be to remove that dependency, and instead rely on Foundation only. That also means that the swift packages now (at least in theory) support all the Apple platforms: iOS, macOS, watchOS and tvOS.