Write a function named even_average which takes an array of integers as a parameter and returns the
average of all even integers in the array.
For example, a call of even_average([1, 2, 3, 4, 8, 7, 6, 6]) should return 5.2
(since only the five values 2, 4, 6, 6, and 8 are considered in the calculation of the average result) and
even_average([5, 4, 3]) should return 4 since 4 is the only even integer in the array.
If the array passed is empty or does not contain any even integers, return 0.
You may assume the array passed is non-null.
