Write a Python script that prints the total number of A's in sequences
given in FASTA format in a file called dna.fasta. The input may contain 
more than two sequences of any length. 

For example if the file contains 

>human
ACCGT
>mouse
GTGATAAA
>cat
GTGA

then the output of the program should be 

6

Your program should work for any sequences and not just the ones in the 
example.

Submit a hardcopy in class on Sept 19th.