return expressions

**Syntax **
ReturnExpression :
   return Expression?

Return expressions are denoted with the keyword return. Evaluating a return expression moves its argument into the designated output location for the current function call, destroys the current function activation frame, and transfers control to the caller frame.

An example of a return expression:

fn main() {
fn max(a: i32, b: i32) -> i32 {
    if a > b {
        return a;
    return b;