Test different hash functions

There are some hash functions that could be faster than stl hash function.

using SMHasher including a STL hash we obtain the next results :

• 255 Hash -> 168 cycles/hash
• 100 Hash -> 94 cycles/hash

City64 -> (from Google, https://github.com/google/cityhash)

• 255 hash -> 108 cycles/hash
• 100 hash -> 70 cycles/hash