Write fizzbuzz(n) returning a list covering 1 to n.
For each number: "Fizz" if it divides by 3, "Buzz" if it divides by 5, "FizzBuzz" if it divides by both, and otherwise the number itself as a string.
So fizzbuzz(5) is ["1", "2", "Fizz", "4", "Buzz"].
Every item is a string, including the plain numbers.