switch from pypi module crc16 to crc

implement redis username uspport

dummy release

allow password for Redis Cluster
allow password for Sentinels

SentinelPool and SentinelHashPool cleanup:

• remove check if client is realy a master or slave

Add HashClient, HashPool and SentinelHashPool

enhancement: Connections Pools can now shrink
bugfix: pass encoding correctly to the protocol parser, if some encoding was set, "utf-8" had always been send to the parser

bugfix. if initial connection attempt failed, mark connection as closed