Write a Python program that prints the score of a given alignment 
according to a substitution score matrix specified in the file 
matrix.txt. The alignment is just of two sequences and is given in
the fle dna.fasta. Use a gap score of -20.

For example if matrix.txt is

        A       C       G       T
A       10      1       -2      -1
C       1       11      2       0
G       -2      2       12      3
T       -1      0       3       9

and dna.fasta is 

>A
ACCGTAAC
>B
ATC---GG

then the program should output the score of -9.
(10 + 0 + 11 - 10 - 10 - 10 - 2 + 2 = -9)

Your program should work even if the user changes a number in matrix.txt
or the alignment in dna.fasta.