Mediator

- Fixed multiple inheritance support.
- Improved venusian support.

- `Mediator.__init__` and `Mediator.scan` now takes keyword arguments only.
- Removed `Mediator.set_scanner` method.
- `Mediator.dispatch()` now takes event instances only.
- `Mediator.add_listener` and `Mediator.remove_listener` takes subclass of `Event` or `str`.
- `Event.get_name()` and `Event.set_name()` were removed in favor of `Event.get_event_name()` and `Event.event_name` class attribute.
- And now there is no requirement to call `super().__init__()` in your own events.

- Added `Mediator.set_scanner` method in order to allow use custom scanner instance.

- Automatic event name detection based on a class name.
- Added `%Event%.listen` decorator.

- First release.