Add Drawable class to the drawing init

Author: DiegoFernandezC

norfair/drawing/__init__.py

@@ -3,5 +3,6 @@
 from .color import Color, ColorType, Palette
 from .draw_boxes import draw_boxes, draw_tracked_boxes
 from .draw_points import draw_points, draw_tracked_objects
+from .drawer import Drawable
 from .fixed_camera import FixedCamera
 from .path import AbsolutePaths, Paths