improve startup time with ConsumeMany()
improve startup time with ConsumeMany()

new sarama or kafka are serializing joining consumer groups, and
for consumers which want to join many topics this is beginning to
take a long time. It seems we can't serially join more than one
topic per 4 or 5 seconds.

So this adds a new API Client.ConsumeMany(topics[]string)
which is logically equivalent to calling Client.Consume(topic string)
over and over, but about as fast as a single call to Consume()

mistsys/sarama-consumer