Maeve Revels

The `Racecar::Producer.shutdown!` method was not actually closing the underlying rdkafka producer, because it was looking for a class instance variable named `@internal_producer` which did not exist. I suspect this stemmed...

The standalone producer includes the topic and partition in the [instrumentation payload](https://github.com/zendesk/racecar/blob/e62b329a69a9274758713e2aa26f55809ed821b5/lib/racecar/producer.rb#L124-L138) for `produce_async` events. However, when the broker acknowledges message delivery, the payload for the `acknowledged_message` event only contains...