* starts 2.3.0 release cycle

updates versions in the configuration tools, bumps up copyright
dates (also normalizes the MIT license to make it recognizable for
github), and updates the release.sh script for the release automation.

* fixes build on macOS

adds the `rm -rf /usr/local/bin/2to3` workaround as suggested in
https://github.com/actions/virtual-environments/issues/2322