[Library Manager] Add FT81x Arduino Driver

[blazer82]

Please add the FT81x Arduino Driver to the library manager: https://github.com/blazer82/FT81x_Arduino_Driver

This is an open source project for a display driver board featuring the FT81x chip. I tried to structure the library according to the guidelines. Please let me know if there's any issues.

[cmaglie]

Done.