Top-k kendall-tau distance. This python module generalise kendall-tau as defined in [1] Fagin, Ronald, Ravi Kumar, and D. Sivakumar. "Comparing top k lists." SIAM Journal on Discrete Mathematics 17.1 (2003): 134-160. It returns a distance: 0 for identical (in the sense of top-k) lists and 1 if completely different.