Almost managed to release this one on the correct date!
This version makes one important change for applications where the canvas is not taking up the whole screen. If the pointer leaves the canvas (Atrament handles the pointerout event), Atrament will now end the stroke, instead of pretending it continues. This helps avoid unexpected stroke paths when returning to the canvas.
Another fix I made was that Atrament now "forgets" the previous mouse position even if the pointerup event fires when the pointer is outside of the element. This prevents unexpected stroke paths when beginning a new stroke.