Adapted from https://github.com/normbxl/USB_PPM_Joystick
Added https://github.com/VICLER/PPMDecoder to it for increased precision.

// D3 / PD3 / INT1 for PPM input
// D2 / PD2 / INT0 used for D+ of USB
// D4 / PD4 used for D- of USB