Updated interface with RX and TX signals

RX_DataReady Flag is no longer latched for a set # of clock cycles. The flag remains latched high until PicoBlaze issues an INPUT sX, PA_DATA_RX request (read incoming RX_data), at which point is will clear the latch.

TX_DataSend Flag is now set and is not cleared until RX_DataReady flag comes in. (Interface will continue to send it's data until it receives new data).