Add initial protocol syntax.

[sigilante]

Target initial syntax:

protocol Arithmetic {
  func add(#) -> #;
  func sub(#) -> #;
};

object Point: Arithmetic {
  let p:(x:@ y:@);
  func init(q:(x:@ y:@)) -> Point {
    p.x = q.x;
    p.y = q.y;
  }
  func add(q:Point) -> Point {
    Point(((p.x + q.x) (p.y + q.y)))
  };
  func sub(q:Point) -> Point {
    Point(((p.x - q.x) (p.y - q.y)))
  };
};

let origin:Point = (0 0);
let vector:Point = (1 2);

origin.add(vector)

Later on, I want to expand protocol syntax and have notes for that, but first let's get it working.