Cubic Bézier curves demo

My attempt at implementing cubic Bézier curves in Pygame. You can drag the points around with the mouse, and use the up and down arrow keys to move the little blob thingy along the path (a quick example of Bézier curves being used as paths). Use the C key to toggle the blob-thing on and off, and the D key to show or hide funky intermediate lines (used in calculating the points on the curve).