[maven-release-plugin] prepare release 0.70
[maven-release-plugin] prepare for next development iteration
Fix outer index joins when multiple overlapping keys are supplied
Add switches to skip and ignore checkstyle.

This should probably go to airbase in the long run. This allows a
submodule to set air.check.fail-checkstyle to false for development,
therefore no longer need to constantly reformat and optimize the code
while developing.
Initial import for Kafka plugin.
Metadata lookup works, topics can be described using json.
update to 0.71-SNAPSHOT, turn off checkstyle