introducing wyhash hash function

[wangyi-fudan]

Dear All:
I would like to introduce wyhash (https://github.com/wangyi-fudan/wyhash)
It is a 64-bit little endian portable hash function as well as a PRNG. It is the fastest one that passed all strict hash function tests (https://github.com/rurban/smhasher) and PRNG test (BigCrush). I think libchaos can make use of it to increase performance.