DATAREDIS-308 - Add support for HyperLogLog.

We added methods for PFADD, PFCOUNT and PFMERGE to RedisConnection and StringRedisConnection. HyperLogLogOperations available via RedisTemplate allow more indrect usage of HLL. 

Please note that currently Jedis is the only driver that can be used for HyperLogLog commands.

Original pull request: #116.