:meth:`.WTaskRegistryBase.tasks` implementation

def tasks(self, task_cls=None):
		""" :meth:`.WTaskRegistryBase.tasks` implementation
		"""
		result = []
		for tasks in self.__registry.values():
			result.extend(tasks)

		if task_cls is not None:
			result = filter(lambda x: issubclass(x, task_cls), result)
		return tuple(result)