Canvas is now stylable through constructor (fill, stroke, stroke_width)
Multiple handlers per event are now supported
Added canvas.all() method (returns all shapes as a list)
New "key" event (keypress while hovering a shape)
New "mclick" event (middle mouse button)
Canvas now scales depending on the window size (optional, see constructor)
Scaling option: keep ratio aspect
Added configurable right-click menu (self.context)