This pull request directs the plugin to configure the jar task (if present, provided by the java plugin) and/or the war task (if present, provided by the war plugin) to set the Implementation-Version and Implementation-Title attributes in the MANIFEST.MF file included in the result.
The end result is that issue #1 (closed) can be satisfied by pulling out Implementation-Version from the MANIFEST. By using MANIFEST, we use a file in Java specifications and we don't have to pollute the build of downstream projects with our own custom properties file.
Manifest reference:
https://docs.oracle.com/javase/tutorial/deployment/jar/packageman.html