I've updated the design to switch from micro-B connectors to C connectors. In principle, this doesn't really change the design very much at all, except to add the two CCx pull-down resistors. The board has to by physically slightly larger but it's not that big a deal.

The TTL variant has also changed to supply all 8 signals rather than just 4. There is now a 10 pin DIP header that has the same pinout as a DTE DB-9 RS-232 connector would, with pin 10 being the power supply pin. Although this is not the industry standard pinout (the so-called FTDI 6 pin connector), it's far more versatile, and you can use SIP jumpers to make any pinout you might want anyway.