Drawing thicker points
POINT seems to be always drawing a 1x1 rectangle:

```lisp
(defun point (x y)
  (declare (type real x y))
  (with-pen (make-pen :fill (pen-stroke (env-pen *env*)))
    (rect x y 1 1)))
```

What if I wanted to increase the thickness of my points instead?  I know I can replace all my calls to POINT with RECT, but what if POINT used the current PEN's _weight_ to figure out how big the rectangle should be?

```lisp
(defun point (x y)
  (declare (type real x y))
  (let ((weight (or (pen-weight (env-pen *env*)) 1)))
    (with-pen (make-pen :fill (pen-stroke (env-pen *env*)))
      (rect (- x (floor weight 2))
            (- y (floor weight 2))
            weight
            weight))))
```

I am happy to open an PR if there is interest in this.