[Feature Request] Kolmogorov-Smirnov test

**Is your feature request related to a problem? Please describe.**
Atm., a Kolmogorov-Smirnov test is missing, for both the two sample test and the goodness-of-fit test.

**Describe the solution you'd like**
Implement such tests.

**Describe alternatives you've considered**
None.

**Additional context**
Be mindful of #89