Return generator by hash generator family name and digest size

		:param family: name of hash-generator family

		:return: WHashGeneratorProto class

def generator_by_digest(family, digest_size):
		""" Return generator by hash generator family name and digest size

		:param family: name of hash-generator family

		:return: WHashGeneratorProto class
		"""
		for generator_name in WHash.available_generators(family=family):
			generator = WHash.generator(generator_name)
			if generator.generator_digest_size() == digest_size:
				return generator
		raise ValueError('Hash generator is not available')