Allow FlexibleSubscriberAdapter to pick-up non-void methods from interfaces

[denis-troller]

The name-based (RegisterMethods()) method subscription allows a non-void method to be picked up so that the method can return an object to be published.

It would be useful for the interface-based version (ByInterface()) to allow the same so that implementers do not have to take a dependency on IBus.

Unless there is an issue blocking this feature ?

[flq]

I'll look into it