Calculate the Damerau-Levenshtein edit distance between two lists (strings).
This is modified from https://wiki.haskell.org/Edit_distance and is originally from Lloyd Allison's paper "Lazy Dynamic-Programming can be Eager"
It's been changed though from Levenshtein to Damerau-Levenshtein, which treats transposition of adjacent characters as one change instead of two.
Complexity O(|a|*(1 + editDistance a b))