Change event isn't triggered if signing continues to outside of canvas

[chrisfnz]

I've identified an issue with this library if drawing a signature and the pen reaches outside the canvas:

1. The jq.signature.changed event isn't triggered until/unless returning the pointer to the canvas and doing a penup / left mouse click.
2. Drawing continues in the canvas even if pen isn't down / left mouse button isn't clicked any more.

I would appreciate your consideration of the the following recommended fixes:

1. Ensure jq.signature.changed event is triggered when-ever leaving the canvas.
2. Drawing once back inside the canvas only works if pen is down or left mouse button is clicked.

Thank you.