BigNum and BigInt timings on the Pollard Rho algorithm

[DougT]

I installed bigints and bignum from nimble. My understanding is that bigints 
(the slower one) is entirely written in nim while bignum is a wrapper for gmp. 
I have not tried bignumber.nim. It appears to be a work in progress. It does 
not have gcd (which I need), although it is easy to write one. When I have some 
time I will give it a try.