Return names of available generators

		:param family: name of hash-generator family to select
		:param name: name of hash-generator to select

		:return: set of int

def available_digests(family=None, name=None):
		""" Return names of available generators

		:param family: name of hash-generator family to select
		:param name: name of hash-generator to select

		:return: set of int
		"""
		generators = WHash.available_generators(family=family, name=name)
		return set([WHash.generator(x).generator_digest_size() for x in generators])