v3.2.0b6

Added

• Documented Stop.NONE and Stop.COAST_SMART.
• Documented ujson, ustruct modules.
• Added done and stalled methods for DriveBase.

Changed

• Changed PrimeHub.display.image() to PrimeHub.display.icon() and renamed
  its kwarg from image to icon.
• Improved presentation and docstrings of the ubuiltins and other
  MicroPython modules
• Moved the random numbers example for Move Hub to the Move Hub page.
• Moved done(), stalled(), load() from Control to Motor object.