[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
*** ./xxhsum 64-bits , by Yann Collet (Nov 27 2014) ***
Loading /tmp/test...
XXH32            : 1073741826 ->  5335.9 MB/s   0xB97A86C1  
XXH32 (unaligned : 1073741825 ->  5626.4 MB/s         
XXH64            : 1073741826 ->  9662.0 MB/s   0x6E8BEE355402863F     
XXH128           : 1073741826 ->  8460.0 MB/s   0x08F69772BFF465696F251EA5F1D49192

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