How to release

Make sure that ~/.m2/settings.xml has your Sonatype credentials.
Increment the version number in the various pom.xml files.
mvn -pl runtime clean deploy -P release
The package should be available within ten minutes, but it might take up to two hours for it to become available at https://search.maven.org/#search%7Cga%7C1%7Cg%3A%22org.capnproto%22
Make a git tag.