Debounced Pushbutton

Implements a class for debouncing a pushbutton.

Other implementations distinguish the events button pressed and button released. In practice, however, button clicked, button clicked twice in quick succession and button held long seem to me to be the most common use cases.

With my solution the user only has to program the methods onClick(), onDoubleClick() and onLongClick() and install them as callbacks of the class DebouncedButton.

Design decisions:

1. The bouncing of the switch lasts no more than 50 ms (a really bad push button)
2. A double-click event is triggered when the second click is made within 250 ms.
3. A click lasts less than 300 ms otherwise a long-click event is triggered.