Add the rest of the hash functions

And a few simple key functions. get => redis_get since 'get' is an erlang reserved word.

redis_get/1, redis_get/2, set/2, set/3,
del/1, del/2, hgetall/1, hgetall/2,
hexists/2, hexists/3,
hkeys/1, hkeys/2, hlen/1, hlen/2,
hsetnx/3, hsetnx/4, hvals/1, hvals/2,
hincrby/3, hincrby/4, hincrbyfloat/3, hincrbyfloat/4