Support Structs

Something along the lines of:

```
; Global scope
Point := (struct (int x) (int y))

; Local scope
{
  pOrigin := (Point 0 0) ; Define a new point on the stack
  (pOrigin x) :<- (+ (pOrigin x) 1) ; increment x
  (pOrigin y) :<- (+ (pOrigin y) 1) ; increment y
}
```
