Add an interface for just getting the matching k-mer coordinates between two sequences

[fedarko]

Not placing them in a matrix -- just returning the match coordinates (given strings s1 and s2 and a value of k) in an easy-to-parse format. Would be useful for @IshaanSD's work.

I'm not sure about what output format would be best -- should we return separate lists of forward, reverse-complementary, and palindromic matches? (Where each "match" is just a tuple of (s1 coord, s2 coord).) Maybe the most elegant option is making some sort of MatchResults class that stores all of these lists of matches.