Py example, draw a white background in a gegl view
Py example, add mypaint surface with gegl backend

- load charcoal brush with mypaint lib
- capture input events and draw on the surface
Py example, do animation with multiple surfaces

- use multiple mypaint surfaces, one per frame
- add key bindings for play, next frame, previous frame
Py example, implement onionskin

two layers are made with nodes 'over' and 'opacity'.
Py example, add timeline widget

drawn with cairo.