replace mersenne twister by pcg

[rurban]

http://www.pcg-random.org/ See branch pcg

First without inlining 6% slower, now with inlining regained the 6% (5a397989846c54d6f3af072be47d3666d331838f) pcg quality is better, but only 64bit.

http://xoroshiro.di.unimi.it/xoroshiro128plus.c is broken.