Driver for "Charlie Plexing" up to 6 LEDs (3 outputs) or 12 LEDs (4 outputs).
(It would be easy to modify to use more outputs)
There's only one procedure to call: CharliePlexing; it may be called from within an interrupt procedure.
Each time the procedure is called, on LED is treated.
The procedure have to be called often enough to have a smooth rendering for the eyes.