Check the forks of the original repository; There are some better implementations.
- https://github.com/progmem/Switch-Fightstick - For the history of LUFA based controller
- https://github.com/shinyquagsire23/Switch-Fightstick - Best application of the original PoC
- https://github.com/tomvdb/avr_arduino_leonardo - UART for atmega32u4
- http://html5gamepad.com - for test!!