GUI coding challenge:

Modify the plus project to include an option to display "big dots".
When this option is selected, mouse motion should draw a 5x5 window
of red at the current mouse location instead of a single 1x1 red pixel.

The following changes need to be made to make this work:
(a) add a new menu element under "display" for "big dots"
(b) add a global variable that keeps the on/off status of big dots
(c) add event handling code that toggles the on/off status
(d) add code at the end of the event handler that updates menu checkmarks
(e) modify the event handling code for mouse motion to draw single pixels
    or big dots depending on the on/off status

extra challenge:

Change the color being drawn depending on if the left mouse button
is held down (yellow) or right mouse button (orange).