USB-UART bridge

A PIC18F14K50 chip can be used as a USB-UART bridge.

After building the electronics and programming it with the USB version of FlashForth,
the BRIDGE word can be used to bridge the UART and the USB interfaces.

: bridge ( -- )
  u1-
  begin
    rxu? if rxu tx1 then
    rx1? if rx1 txu then
  again
;