* Add the Pimoroni Servo 2040 board
This PR adds the board support package and two simple examples.
* Animates a rainbow wheel across the RGB LEDs on the board.
* Moves a servo that's connected to GPIO0 back and forth.
* Format pimoroni-servo2040 board files
* Use us_to_duty function in servo example, clean up comments.
* Fix bad types
* Add Servo2040 description to top-level readme
