title: Can Kafka message consumed by different consumers?
body: <p>I am new to Kafka. I have produced a kafka message named foo by <code>kafkaSink</code> ,a class in <code>Flume</code>.When I want to  consume the messages,many questions come unclear to me:
  1.I have tried to use <code>kafka-console-consumer</code> to consume <code>message foo</code>,and it succeeded.Can I consume <code>message foo</code> again with another consumer process somewhere else?
  2.To the opposite,I don't want to consume <code>message foo</code> again, so when I try to consume with another consumer,I should obtain nothing.How can I achieve this?
  3.What if there are two messages <code>foo</code> and <code>bar</code>.Can I specify consumers precisely?(For example,I want process A consumes <code>message foo</code> and process B consumes <code>message bar</code>.To go further ,can O specify a range of message offsets? Does it have something  to do with <code>consumer group</code>?</p>