DNA analysis

DNA is represented by an alphabet of the following symbols: ‘A’, ‘C’, ‘G’, and ‘T’. Each symbol represents a nucleotide, which is a fancy name for the particular molecules that happen to make up a large part of DNA. DNA contains four types of nucleotide, namely adenine (A), cytosine (C), guanine (G), and thymine (T), and hence the symbols.

Your task is then to implement a function that counts the number of occurrences of one nucleotide on a given a DNA string (well, in this exercise, we use Elixir charlists as input a not strings).

You can find the skeleton of the application here.