Small example to show how to use render_to_png inside a glut application.

Compile with:

make

Run with:

./example

Then hit [space] to take a screen shot. Hit 's' to change the shape.

Produces files in the working directory named:
render_to_png-example-example-0000.png,
render_to_png-example-example-0001.png,
and so on
