v3.0.0-beta.1: more flexibility

This release brings more flexbility.

✨ Features

• Set the course time after instantation
• Set a different up and down course time (#11)
• Ability to set the same callbacks for multiple shutters (a pointer to the affected Shutters instance is passed to the callbacks)
• The state is now stored as a char array. This makes it easier for some platforms to store the state (some platforms don't manage 64bits integers)