v2.0.0: Non-blocking

This release brings non-blocking code, even if the shutters state is not known.

✨ Features

• Non-blocking
• Storage is now abstracted using callbacks
• A little "delay" (non-blocking) is introduced between up, down and halt calls to avoid switching too fast mechanical relays, for example
• Optimize movements: don't call halt if setLevel(100) is called while already going down