Version 1.0.1.0: FST fix and better user input checks

This release fixes a bug in the estimation of FST. We have now exactly implemented the estimator presented in Bhatia et al. 2013
(see whitepaper), and confirmed numerical equivalence with estimation by admixtools.

We have also now checked for degenerate statistics (for example F2(A, A) or F3(A, B, A)) and in those cases now output exactly zero.
Previously, due to bias corrections, results could become negative.

Finally, we have implemented a check for illegal sample sizes. In particular for F3(A, B, C), where C is a haploid outgroup, we now
throw a helpful error that one should rather use F3vanilla, since F3 in that case is undefined due to its use of the heterozygosity of
C in the bias-correction term (see whitepaper).