* update version to 2.4.0

* Add version options to config file.

* update resource

* add  message version support  for dashboard

* add  message version support  for dashboard

* Support using version to isolate messages. #220

* update mongo unit tests

* update unit tests

* update unit tests

* Set default versions for consumer groups

* solve the problem of issue#181 (#237)

* Issue#235 (#238)

* solve the problem of issue#181

* solve the problem of issue#235

* refactor

* Fix the message persistence bug. #240

* using new CamelCaseNamingStrategy

* update packages to .net core 2.2

* update test framework to netcoreapp2.2

* Update .travis.yml

* update TargetFramework

* Exclude build samples project

* fixed message enqueue exception in v2.2

* add log to samples

* Improved log output.  #114

* add default timeout configuration for kafka client.

* fixed retry processor bugs.

* Fixed kafka producer exception log without logging when publish message.

* update version num to 2.2.2

* rename configuration options FailedCallback to FailedThresholdCallback

* rename files name.

* remove unused files.

* modify the error comments.

* update samples.

* add logs.

* fixed message enqueue exception in v2.2

* add log to samples

* Improved log output.  #114

* add default timeout configuration for kafka client.

* fixed retry processor bugs.

* Fixed kafka producer exception log without logging when publish message.

* update version num to 2.2.2

* rename configuration options FailedCallback to FailedThresholdCallback

* rename files name.

* remove unused files.

* modify the error comments.

* update samples.

* add logs.