Creates a png file with the current phase of the moon

 This program is intended as a successor to the xphoon program (X PHase of
 mOON). xphoon is a program that displays the actual phase of the moon on the
 X11 root window. Nowadays many desktop systems like KDE hide the X11 root
 window with a background image of their own, so the xphoon output is not
 visible. When called, pngphoon creates a PNG image with the current phase of
 the moon. It can be used with window managers that allow using a command to
 provide a background image.