Aioredis-cluster

------------------

* Library full rewrite
* Cluster state auto reload
* Command failover if cluster node is down or key slot resharded

------------------

* Pipeline and MULTI/EXEC cluster implementation with keys distribution limitation (because cluster)

------------------

* Python 3.6+ only

------------------

* Initial release based on aioredis PR (https://github.com/aio-libs/aioredis/pull/119)