Write a Python program that prints the number of A's, C's, G's, and T's in 
a user specified column as a percentage of the total number of sequencs.
For example if the multiple alignment below is given in dna.fasta and the
user enters column 1 on the keyboard then the output should be

>human
ACCT
>mouse
ACGT
>cat
TCCT
>dog
ACAT

the output should be 

A: 75%
T: 25%

If the user enters column 3 then the output should be

A: 25%
C: 50%
G: 25%

You solution should work for any number of sequences and any 
sequence length. Submit your solution in class on Dec 2nd.