wallknob: Use a callback function to allow changing event handler
wallknob: Move left/right key mapping code to a generic place
wallknob: Avoid triggering handle_button_press outside expected key presses
wallknob: Split out blocking single-event fabdwk_wait_for_event function
wallknob: Move reasonably-sharable stuff to a header
wallknob: Text menu with choices to select
wallknob: Make units configurable via menus
wallknob: Ignore key presses from devices of unknown type
wallknob: Calibrate knob turning to work nicely
wallknob: Adjust initial scroll to top of first menu item
wallknob: Default units prompt to current value