[RIP-9] enhance description about the state "SLAVE_NOT_AVAILABLE" in the chinese version of "best_practice.md" (#867)

[RIP-9] Add API_Reference_DefaultMQProducer.md for Java

* add english document of transaction message design

* Format the style.

[RIP-9]add the design content of RocketMQ doc part.

[RIP-9]Add the features of RocketMQ into the develop guide for users

* [RIP-9]add the msg trace of RocketMQ doc part

* [RIP-9]add the acl feature of RocketMQ doc part

* [RIP-9]adjust the title number of the acl feature doc part for RocketMQ

2. Corrected some typos
3. Introduce of the Schedule Message

same indentation
OpenMessaging

2. Order Example
3. Schedule Example
4. Batch Example
5. Filter Example
6. Transaction Example
7. Logappender Example
8. OpenMessaging Example