Extract `buildSrc` to separate repo if possible
buildSrc contains the code to make the task
RelastTest available in the Gradle build script. It must to be at the root of the repo.
In this repo, @rschoene simply copied the contents into this repository, but having a separate repo would allow reuse over multiple projects (this and relations-rags, as a start).
Furthermore, it could be enhanced to extend the
clean task to remove all generated files.