Allow producing Kafka message without a key
In this release, a few things have changed:
- The project is re-licensed to Apache 2.0, so it can be run on the cloud.
- Thanks to @eduardowitter, PR #30 is merged that allow producing Kafka messages with no keys.
- README is updated with some useful troubleshooting instructions.
- A blog article is published on k6 blog to demonstrate the capabilities of the extension.