add Random.Xor128, pseudo random number generator using xorshift

Vital.Random.Xor128 provides a Random Number Generator(RNG) using a xorshift
algorithm. Although xorshift has a reasonable period(2^128-1), it is fast and
has less internal states.
The paper about xorshift is http://www.jstatsoft.org/v08/i14/paper .
Merge pull request #107 from rhysd/add/xorshift

add Random.Xor128, pseudorandom number generator library