simplify separation between sync and async producer implementations via inheritance
simplify separation between sync and async producer implementations via inheritance

benauthor/pykafka,sammerry/pykafka,aeroevan/pykafka,yungchin/pykafka,benauthor/pykafka,jofusa/pykafka,yungchin/pykafka,thedrow/samsa,wikimedia/operations-debs-python-pykafka,wikimedia/operations-debs-python-pykafka,wikimedia/operations-debs-python-pykafka,benauthor/pykafka,thedrow/samsa,jofusa/pykafka,sammerry/pykafka,thedrow/samsa,aeroevan/pykafka