[RFC PATCH] Add 128bit xxhash function

For some tasks one needed hash value what biggest then 64 bit (128, 256...)

Use as base 64bit function, working on the comparable speed:
[$]: fallocate -l 1G /tmp/test
[$]: ./xxhsum -i3 -b -H3 /tmp/test


Also it a good example for create big hashes for another tasks

Signed-off-by: Timofey Titovets <nefelim4ag@gmail.com>

P.S.
I just want to hear comments, code can be ugly and may be useless.

P.P.S
After deletion return values from XXH128_* functions speed can be 1 in 1 as for naked 64bit hash and i preferable make this functions void