NEW: Added a stack of states
NEW: Added finish() to states, so states can terminate themselves
NEW: Added an event, onFinished(), that can be triggered with notifyFinish()

fixes #5
NEW: Replace DigitalOutput with BlinkyLight.

Commands can now be represented as NightlightStates, thanks to state finishing and the state stack. The DigitalOutput class is a bit obsolete, so I’ve removed it.

Example has been updated.