GUI coding challenge #2:

Modify the plus project to display an "explosion" when the left or
right mouse button is pressed.  The explosion should draw a red box
centered at the current mouse location.  The box should grow from
a 7x7 (width=3) to a 61x61 (width=30) over time.

Implement the explosion using a thread.  The thread can retrieve
the starting location of the explosion upon starting, but should use
local variables for all drawing.  This way the thread can be called
multiple times.  The thread should terminate when the box reaches
max size.

extra challenge:

Change the shape being drawn depending on if the left mouse button
is pressed (square) or right mouse button (circle).