better inheritance: inherit: true will really reuse the parent Definition instance (or, a clone thereof) making it better following ruby's object model.
don't pass inherit: into merge! anymore.
remove Def#call_proc_for, which was the intended goal of this refactoring.
introduced `:use_decorator` option to force an inline representer to be implemented with a Decorator even in a module. This fixes a bug since we used the `:decorate` option in earlier versions, which was already used for something else.