:meth:`WCacheStorage.clear` method implementation (Clears statistics also)

def clear(self, decorated_function=None):
		""" :meth:`WCacheStorage.clear` method implementation (Clears statistics also)
		"""
		if decorated_function is not None and decorated_function in self._storage:
			self._storage.pop(decorated_function)
		else:
			self._storage.clear()

		if self.__statistic is True:
			self.__cache_missed = 0
			self.__cache_hit = 0