[Feature Request] Dunnett's test

**Is your feature request related to a problem? Please describe.**
Post hoc tests are used to inspect a multipe-group-comparison (e.g. ANOVA) for individual significant group mean differences.
While Tukey's HSD aims to perform all comparisons k((k-1)/2), it often is desired to test all groups against a single control or standard.

**Describe the solution you'd like**
Dunnett's test allows this multiple-to-one comparison with higher power than Tukeys HSD.

**Additional information/References**
https://www.researchgate.net/post/What_is_the_difference_between_Tukeys_Post_Hoc_Test_and_Students_t-test