Adding the UART downstream serial port interface. This takes the packets
and sends/receives the data. I also looped back the send with the rx
stream to test that in parallell.
Adding the downstream stream functions by passing the fifo, makes it
much easier...

#18
Downstream path to serial port is confirmed, but now its getting jammed
on the avr-pic up path. I see it comming into the pic with 'method
unknown'. close #18