I wanted to write a program which will draw centric circles. It then
starts drawing a filled circle at the center with the initial size of
4 pixels. The circle will grow in the rate of 1/4 of it current size.
Whenever, the current size of a circle is bigger then the initial
size, a new circle with initial appears at the center. When the outer
most circle reaches the border of the displayable window, it will
reappear at the center with the initial size. Every circle must have
a random color and this color will stay with that circle through out
its lifetime.

The maximum number of circles will be drawn can be computed by the
grow rate of a circle, the initial size of the circle and the window
size. (It's 25 circles if the windows size is 500.)