perf(binomialDistribution): avoid expensive factorial calculations (#205)
perf(binomialDistribution): avoid expensive factorial calculations (#205)

Improves performance of binomialDistribution by computing binomial
coefficient cumulatively instead of using factorials in each iteration.

Ref #194
simple-statistics/simple-statistics,tmcw/simple-statistics,simple-statistics/simple-statistics,simple-statistics/simple-statistics