* 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.

* Fixed the connection bug of getting message from table. #83

* update version to 2.1.4

* remove `TableNamePrefix` option from `MySqlOptions` to `EFOptions`.  #84

* fixed entityframework rename table name prefix bug.  #84

* fixed sql server scripts bug of create table scheme. #85

* fixed entityframework rename table name prefix bug. #84

* modify error message of logger write

* Fixed bug of the FailedRetryCount does not increase when raised SubscriberNotFoundException. #90

* Fixed thread safety issue about KafkaOptions. #89

* upgrade nuget package