Optional graphics

This example shows how to easily write an app that can be ran in both graphic and non-graphic mode, with the decision delegated to the code based on whether "empty" was used as a feature. Handy for applications which want to support raw-console mode.

It borrows most of the code from the window example.

Keybindings:

• Esc or q - Quit in graphic mode. For non-graphic mode there will be no window, so press ctrl-c in the terminal to terminate the example.