More usability API

[wenfengwang]

FEATURE REQUEST

1. Please describe the feature you are requesting.
   make API more usability and follow the standard of Go

2. Provide any additional detail on your proposed use case for this feature.

• Functional Options
• Separate logic and data-struct
• Minimize functions in each API

3. Indicate the importance of this issue to you (blocker, must-have, should-have, nice-to-have). Are you currently using any workarounds to address this issue?
   must-have

4. If there are some sub-tasks using -[] for each subtask and create a corresponding issue to map to the sub task:

   • Functional Options: Using private config members to protect them
   • Separate logic and data-struct: move all public data-struct to an independent package
   • Refactor APIs: refactor APIs of Producer/PushConsumer/PullConsumer

[wenfengwang]

#103 merged