SpanButton now instantiates PushButton instead of keeping track of its own triggering logic. This means that SpanButton longPress() is triggered by holding down the button for longTime WITHOUT the need to release. This is a desired change.
Next: Must update Example 15 to state that SpanButtons trigger a long press withouth needing to be released.
To do: Consider adding a "repeating mode" for longPress in which the SpanButton re-triggers every longTime while button continues to be pressed. Best way to implement is probably by creating a PushButton::extend() method.
Gregg