Hazelcast Jet 4.1 is released

[Can Gencer]

I'm happy to announce Jet 4.1 is released.

See the notes below and thanks to all the contributors.

* You can now use our JMS and JDBC sinks with the exactly-once guarantee.

* We simplified adding classes to the Jet job configuration object. You

  can add a whole package in one call and, for `jobConfig.addClass`, we

  automatically add all the class's nested classes, including anonymous

  ones.

* We made the serialization setup simpler. You can now register custom

  serializers with the job and we added extra convenience for protobuf

  serialization.

* We added a `ServiceFactory` that accesses an external gRPC service. You

  can now use `mapUsingService` to transform the data by calling either

  a unary or a bidirectional streaming gRPC service.

* We added the `innerHashJoin` transform that achieves an inner join

  directly instead of requiring custom code in the `mapToOutputFn`. Credit

  for this one goes to @TomaszGaweda.

See the blog post for more details about each feature: https://jet-start.sh/blog/2020/04/29/jet-41-is-released