A number is said to be Harshad if it's exactly divisible by the sum of its digits. Create a function that determines whether a number is a Harshad or not.
isHarshad(75) ➞ false
// 7 + 5 = 12
// 75 is not exactly divisible by 12
isHarshad(171) ➞ true
// 1 + 7 + 1 = 9
// 9 exactly divides 171
isHarshad(481) ➞ true
isHarshad(89) ➞ false
isHarshad(516) ➞ true
isHarshad(200) ➞ true