[ISSUE #608] Polish simple example

[RongtongJin]

What is the purpose of the change

Fix issue608
Polish simple example

Brief changelog

• simple
  • AsyncProducer.java (add code comments)
  • OnewayProducer.java (new class, show users how to send meassges in oneway)
  • PullConsumer.java
  • PullScheduleService.java (no change)
  • PushConsumer.java (Setting ConsumeTimestamp is invalid when you set ConsumeFromWhere to CONSUME_FROM_FIRST_OFFSET, so I delete releated code)
  • QueryMsgByKey.java (renamed from TestProducer.java, a clearer class name)
  • SyncProducer.java (renamed from Producer.java)
  • RandomAsyncCommit.java(remove this class. It doesn't show the users how to send or receive messages, and it also doesn't involve client code of RocketMQ)
  • CachedQueue,java (remove this class used in RandomAsyncCommit.java)
  • PullConsumerTest.java (remove this class. The code is similar to PullConsumer.java)

[coveralls]

Coverage decreased (-0.07%) to 43.112% when pulling 6fdb0d1 on RongtongJin:polish_simple_example into 385c695 on apache:develop.