v0.19

This is our first release to Maven Central - documentation is still lacking, testing is a bit rough around the edges, and performance could definitely be improved. The next two versions seek to tackle these issues, along with wider adoption to ensure that we've covered important use cases.

See https://github.com/Vertispan/j2clmavenplugin/milestone/1 for more details on what was specifically targeted for this release. Going forward we will use github release tracking to generate proper release notes, but it did not make sense to use the generated list for the initial tagged release.