Change AVRISP project's timeout to be interrupt based again, but make the interrupt...

Change AVRISP project's timeout to be interrupt based again, but make the interrupt itself interruptable and use a seperate assembly file to hand-optimize the ISR code.

Removed the cast to uint16_t on the set baud rate in the USBtoSerial project, so that the higher >1M baud rates can be selected (thanks to Steffan).