Step 1. Make a file called library.php
Write a function called isEven that takes in a variable and returns true or false if the provided input is evenly divisible by two or not.
Write a function called isVowel that returns true or false if the provided input is the letter 'a', 'e', 'i', 'o', or 'u'
Write a function called "first" that takes in an argument that could be an array or a string. Return the first character if the argument is a string. Return the first element of the array if the input is an array.