Started implementing the low level PDI protocol in the AVRISP project, for XMEGA device programming.

Add new more reliable software UART for the XPLAINBridge project by David Prentice and Peter Danneger.

Removed John Steggall's software UART code from the XPLAIN Bridge project due to reliability issues.

Enable pullup on the PD5 pin of the AVR in the XPLAINBridge project - this is connected to the XMEGA's /RESET line, need to enable pullup to prevent spurrious resets.