Methods for automatic initial entropy generation and caching

[KOVALW]

There's a tendency to use small integer seeds for initializing RNGs, such 12345. However, the bits in these integers do not allow for sufficient space exploration (see here).

We should offer a convenience method to sample the current system entropy using hex(SeedSequence().entropy), checks for confirming entropy when initializing the sampler, caching for truly stochastic runs of the sampler, and docs explaining these concepts to users.