Add a split screen example using Camera2D

[MiCurry]

This is a simple example of how to create a split screen example using Camera2D and uses the PyMunk physics engine.

In the example, we create two cameras, and change their viewports to be half of the screen. When drawing the scene, we loop through each camera and draw our scene, then in update() we center the cameras on the players. We also use the default camera to draw a divider.

It also contains other useful examples, such as zooming out the camera, and resizing the split-screens when the window is resized.

[MiCurry]

I wanted to suggest this example as I believe a split screen example would be popular. This example might be better instead if it uses the simple physics engine and if uses the same 'map' as the other examples in the Camera section (e.g. Sprite-move-scrolling).

Happy to change it to use the simple physics engine, and make any other changes!