fix top mounting hole: was 5mm, should be 6mm

move right_13_down and left_13_lt a few millimeters up For less strain on the FPC cables, on both KB500 and KB600.

README: describe possible teensy combinations

update artifacts

update PCB revision

update schematic revision

make some space at the edges of the PCB

square cutouts

fix KB600 pinout

add molex FPC part number to silk screen