Support for PFADD , PFCOUNT from spark

[nirmalc]

Adds two functons:

fromRedisHLL - to read data from redis HLL to (RDD[String,Long)] using key
key pattern

toRedisHLL - Adds ( pfadd) to Redis HLL from RDD[(String,String)]

[nirmalc]

is Travis config broken ? Getting a redis compilation err..

/home/travis/build/RedisLabs/spark-redis/redis_for_spark-redis_test/deps/jemalloc/src/nstime.c:120: undefined reference to `clock_gettime'

[justinrmiller]

@nirmalc @fe2s @gkorland I think this functionality would be great to have. Is the only thing holding this up merge conflicts with master? If so I'm happy to branch master and get these changes added if @nirmalc doesn't want to go through adding it all again.

[fe2s]

@justinrmiller , agree this might be valuable even though spark has its own implementation of HLL. This is quite an old PR and was probably overlooked.