[Feature Request] X² test for 2×2 contingency tables

**Is your feature request related to a problem? Please describe.**
An often used variant of the X² (Chi-squared) test is that for 2×2 contingency tables (aka Cochran-Mantel-Haenszel test). Since the original X² test is already implemented, a version for 2×2 contingency tables can easily be implemented.

**Describe the solution you'd like**
Implement it.

**Describe alternatives you've considered**
Always write it yourself with the already existing X² test.

**Additional context**
https://en.wikipedia.org/wiki/Cochran%E2%80%93Mantel%E2%80%93Haenszel_statistics (eng)
https://de.wikipedia.org/wiki/Chi-Quadrat-Test#Vierfeldertest (ger)