RPC support

[Marthym]

Do you plan to support RPC exchanges ?

Actually in the code

    @Override
    public CompletableFuture<Command> asyncCompletableRpc(Method method) {
        throw new UnsupportedOperationException();
    }

[ledoyen]

I did not know that there was a need for that 😃

I do not see any problem for implementing this, except I do not have much time to actually do it (given that it will require some refactoring in existing stubs to avoid duplicating logic).

I will be happy to review any PRs if you want to give this a try.

[RedMu]

I have a usecase for this, so I could pick this up.