improvements, part 6

this is the final update for now. it fixes all known bugs and improves balancing/progression.

✱ limited Plus cards to 1 per turn
✱ updated enemy generation to ramp up the difficulty gradually
✱ game has an end now
✱ raised chance of enemies using cards
✱ fix glitch sprite and loot drop order when multiple enemies go down on the same turn
✱ fix 'cards drafted' counter to include loot drops & cloned cards
✱ edited title screen icons
✱ fix Credits card playing sound multiple times
✱ fix music continuing past reset
✱ added transition animations to title screen & drafting