Improve micro:bit support and add examples

[Fabien-Chouteau]

This PR improves our micro:bit support with features like:

• Analog output
• Accelerometer
• Music

and add examples for most of the features of the board.

To review the examples, it is better to look at them with a nice markdown render:

• Text Scrolling
• Buttons
• Digital Output
• Digital Input
• Analog Output
• Analog Input
• Music
• BLE beacon

[Fabien-Chouteau]

Thanks @pat-rogers