Uses the Levenshtein Distance algorithm (https://en.wikipedia.org/wiki/Levenshtein_distance) to calculate the edit distance between two NSStrings. Based on https://gist.github.com/wewearglasses/1593632.
Usage:
[@"한글" levenshteinDistanceFromString:@"자글"];
Note: emoji characters are treated as length 2, so [@"🌈" levenshteinDistanceFromString:@"🌈🦄"] returns an edit distance of 2.