adding ability to detect handlers from super class.

[thirogit]

When handler class is annotated with @InheritSubscribers during registration all DECLARED handler methods from super class will be added to subscribers list. Handled methods from superclass's superclass
will not be added unless it also has @InheritSubscribers annotation.

As this functionality is explicitly requested by the user by placing InheritSubscribers annotation,
user cannot complain on performance and code complexity.

[JakeWharton]

We're just going to enable this for all types by default. Opt-in not necessary. See #135.