Write a function named gcd that accepts two integers as parameters and returns the greatest common divisor of the two numbers.
The greatest common divisor (GCD) of two integers a and b is the largest integer that is a factor of both a and b.
One efficient way to compute the GCD of two numbers is to use Euclid's algorithm, which states the following:
GCD(A, B) = GCD(B, A % B)
GCD(A, 0) = Absolute value of A
In other words, if you repeatedly mod A by B and then swap the two values, eventually B will store 0 and A will store the greatest common divisor.
For example: gcd(24, 84) returns 12, gcd(105, 45) returns 15, and gcd(0, 8) returns 8.
