* Improve the implementation mechanism of queue mode. #96
* refactor the code .
* add Copyright & License description into header text of code files.
* refactor
* set version to 2.2.0
* update unit tests.
* add exception class to process the publish send and subscriber exectution exception
* modify first retry time to three.
* code refactor.
* add retry mechanism
* code refactor
* refactor consumer execution
* fix spell error
* remove dashboard `processing ` content.
* Modify the retry to retry the message only 4 minutes ago.
* update samples
* update ci configuration.
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