Version 4! Now with mechanism.

Version 4 is super awesome! It has 0.8 thick walls (that means two
passes of the 0.4 mm ultimaker nozzle. it only works with a 0.4 mm
nozzle)

Being 2 passes thick, the whallet is now pretty flexible, which means it
actually works super well in your pocket.

Also, there's two little 'fingers' in the bottom that clamp down on the
cards when they're pushed down, preventing the cards from sliding out.