RxLogObservable annotation for entire class.

Hi Fernando. Thanks for this awesome library :)

I've just integrated it in my current project and it works perfectly. The problem is that I needed to annotation like 50 methods xD

I've annotated every `public` method for every one of my repositories (and most of their methods have a `public` visibility). So, I think it will be nice to have an `annotation` with target `ElementType.TYPE` in order to be able to annotate an entire class (or repository for that matters), and selecting the methods to be logged based on the visibility scope selected (by default only `public`).

Do you think this is is technically possible? And if so, would you accept a PR -previously discussing the api?