Hardcoded timeout in USB_Send

[Ryzee119]

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Here: u8 timeout = 250

250ms is quite large for my application. Could this be moved to a compile time define?

Perhaps something like this?

#ifndef USB_SEND_TIMEOUT
#define USB_SEND_TIMEOUT 250
#endif

- u8 timeout = 250;		 // 250ms timeout on send? TODO
+ u8 timeout = USB_SEND_TIMEOUT; // timeout on send? TODO

[Ryzee119]

I raised a quick patch for this change https://github.com/arduino/ArduinoCore-avr/pull/479