Add a write method to the JSONPrettyPrinter class to output a character.
This will be used to handle state updates when outputting individual
characters.
Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: David Plowman <david.plowman@raspberrypi.com>
Tested-by: David Plowman <david.plowman@raspberrypi.com>