Test project to try out Maven Toolchains

and how to get it all running in Github actions and Gitlab-CI.

This project shows:

• Building and testing using toolchains.
• Building a multi release jar.
• Testing a multi release jar with the same integration tests under multiple JDKs.

Same project on 2 platforms:

• https://github.com/nielsbasjes/ToolChainsInCiBuilds
• https://gitlab.com/niels/ToolChainsInCiBuilds