Support CLUSTER SLOTS command

* CLUSTER SLOTS returns a Redis-formatted mapping from slot ranges to IP/Port pairs serving that slot range
* description link including output format
** https://github.com/antirez/redis/commit/e14829de3025ffb0d3294e5e5a1553afd9f10b60
* Unit test included
Merge branch 'support-cluster-slots' of https://github.com/HeartSaVioR/jedis into HeartSaVioR-support-cluster-slots