Modify the NWscore function from homework 2 to use the
BLOSUM_62.txt substitution scoring matrix provided on the
course website. Instead of match and mismatch cost use
the substition scores from the BLOSUM 62 matrix. Store
the matrix as a dictionary where keys are pairs of amino
acids and values are the corresponding BLOSUM 62 scores.

Submit hardcopies in class on Feb 11th.