anchor: love.joystick.getGamepadMappingString
  Gets the full gamepad mapping string of the Joysticks which have the given GUID, or nil if the GUID isn't recognized as a gamepad.
  
  The mapping string contains binding information used to map the Joystick's buttons an axes to the standard gamepad layout, and can be used later with love.joystick.loadGamepadMappings.
  mappingstring = love.joystick.getGamepadMappingString( guid )
  guid string The GUID value to get the mapping string for.
  mappingstring string A string containing the Joystick's gamepad mappings, or nil if the GUID is not recognized as a gamepad.