It's a USB Type-C connector just like the one used in v0.1 and v0.2, but
with only SMT pins (except the fixing pins, of course).  They're
slightly cheaper and probably nicer for automated assembly, but
impossible to hand-solder.  That's okay though: where we're going, we
don't need hand-solderability.

There was previously no way of seeing where the business end of the USB
connector was.  To solve this, I added a crude outline of the connector
on the F.Fab layer.

Tested to probably not blow anything up if assembled properly!