Add Arduino UNO R4

[kingprofire]

Arduino UNO R4 Minima & WiFi now support USB HID. It would be great if I can use this library with the R4 board.

[MHeironimus]

I just released an update to the legacy version (non-configurable) of this library that supports the Arduino UNO R4 boards. You can see and download this version at https://github.com/MHeironimus/ArduinoJoystickLibrary/tree/version-1.0.

If you test it out, please let me know how it works for you.

It will take me some time/effort to update the current version (which is configurable) to support the Arduino UNO R4 boards, so I updated the older, simpler version of this library first as a test and to verify what needs to change in the current version.