Optionally add TestU01 tests

[rurban]

check for the libtestu01.a (preferred my fork with fixes https://github.com/rurban/TestU01)
and run the tests provided there.

[o0101]

That's a great idea.

I've used Dieharder and don't think I've used TestU01. I know you're super busy and sorry for the question, but in your opinion what's the difference?

[rurban]

TestU01 has a nicer API, in C. It can run single statistical tests, or a crush suite. But I'm not sure yet. Fixing it took a whole day

[peteroupc]

In general, it would be good to do randomness testing to show which hash functions are good choices for a counter-based PRNG construction, in which an incrementing counter and a seed are hashed together to produce pseudorandom numbers ("Parallel Random Numbers: As Easy as 1, 2, 3", 2011). See my note on testing PRNGs, especially the section "Hash functions and counter-based PRNGs".