Rpm spec

Simple RPM spec to construct a RPM out of kafkacat. It requires the RPMP provided in librdkafka. For future reference for RPM builders, this is the trick to build a tar.gz

git archive --format=tar.gz --prefix=kafkacat-1.1.0/ 1.1.0 > ~/kafkacat-1.1.0.tar.gz
Okay, but then you will want to perform the tee output after the produce request has been acknowledged by the broker. The produce() call is async, all it does is enqueue the message internally in librdkafka, there is no guarantee that the message will be succesfully delivered.
So what you want to do is register a delivery report callback and tee the message from there.
I can make those modifications after merging this PR.