Add support for Brunner-Munzel test

[kidotaka]

https://docs.scipy.org/doc/scipy/reference/generated/scipy.stats.brunnermunzel.html

From scipy doc.

The Brunner-Munzel test is a nonparametric test of the null hypothesis that when values are taken one by one from each group, the probabilities of getting large values in both groups are equal. Unlike the Wilcoxon-Mann-Whitney’s U test, this does not require the assumption of equivariance of two groups. Note that this does not assume the distributions are same. This test works on two independent samples, which may have different sizes.