Add a "num1 ** num2" operator as a shortcut for pow(num1, num2)

[Runemoro]

Adding an exponentiation operator, like ** in python, would make code more readable and faster to type. The way it works right now, it's easier to type x * x * x (5 characters) instead of pow(x, 3) (8 characters).

Also, it makes more sense to use an operator rather than a function, since we usually use infinix notation with exponentiation, as well as addition, subtraction, multiplication and division (we write a + b, a * b, a ^ b instead of sum(a, b), product(a, b), pow(a, b)).

[zoechi]

Dup of #1859