Attack/Defense Counters

Plus one/one, plus one/zero, and minus one/one counters to keep track of counters applied in card games.

Modified https://www.thingiverse.com/thing:3067562/comments by https://www.thingiverse.com/jlgilmon/designs

Removed overhang from edges of counters to allow printing to be easier on lower end printers, and shrunk the size slightly to have more reasonable scaling with cards.