Key hash calculation.

There are next possible ways for cache calculation.

1. Update hash on every write method call as it works for now.
2. Calculate for all key chunk (hash of byte[]) - all columns including a null-map.

Let's choose and implement the best way and along with a better hash function,
e.g. xxHash64 [1], Murmur3 [2]released in Apache Commons, CityHash (from Google) [3], FastHash32 [4].

[1]https://github.com/Cyan4973/xxHash/

[2]https://commons.apache.org/proper/commons-codec/jacoco/org.apache.commons.codec.digest/MurmurHash3.java.html

[3] https://github.com/google/cityhash

[4] https://github.com/rurban/smhasher/blob/master/fasthash.cpp