Write a method called digitSum that accepts an integer as a parameter and returns the sum of the digits of that number. For example, the call digitSum(29107) returns 2 + 9 + 1 + 0 + 7 or 19. For negative numbers, return the same value that would result if the number were positive. For example, digitSum(-456) returns 4 + 5 + 6 or 15. The call digitSum(0) returns 0.