Function to summarize bases at a given position in a fasta file

Added a function to take a fasta file with sequences and a position and return information about which bases / amino acids are found at that position.
Sorry to do it on my master, I got over exited...
You'll only need to return `countAtPosition` if you make the `summarizePosition` function a method of the reads class. Then `summarizePosition` will only have to do one job.