Clean-up: docs, error handling, old cruft.
Clean-up: docs, error handling, old cruft.

Factor now doesn't fail.

huonw/slow_primes,wackywendell/primal,cuviper/primal,cuviper/primal,huonw/primal,huonw/primal,wackywendell/primal,Antiarchitect/primal,Antiarchitect/primal