Write a function power(base, exponent) that returns the value base^exponent, i.e. base * base * base * ... * base, where there are exponent many terms of the product. For example, 2^5 = 32 because 2*2*2*2*2 = 32. Do not assume base and exponent are integers. Raising a number to the power 1/2 is the same as taking its square root.