Add support for static methods

[wiseodd]

Use the class keyword preceding the method to indicate a static method that hangs off the class object.

class Math {
  class square(n) {
    return n * n;
  }
}

print Math.square(3); // Prints "9".

The “metaclasses” used by Smalltalk and Ruby are a particularly elegant approach. Hint: Make LoxClass extend LoxInstance and go from there.