****ToDo****
------------

Primary Shot Pickups
--------------------
- Stealth shots.
- Giant shots.
- Bullets collide with other bullets?
- Shots destroy walls.

Secondary Shot Pickups
----------------------
- Laser barriers (kill on touch).
- Clones (rudimentary AI tanks, visually identical to player's).
- Bullet vortex?
- Stealth mines.

Tank pickups
------------
- Cardinal mode (can only move in the 4 cardinal directions, no turning).
- Stealth tanks.
- Force field (1 hit drops the field; recharges and reappears; cumulative).
- Drone (Death Ray Manta-style drone follows tank, shoots in opposite
  direction).

Level Pickups
-------------
- Add walls.
- Movable walls (walls will move when pushed, fired upon etc.).
- Wrap level horizontally.
- Wrap level vertically.
- Dancing walls (walls dance, move tanks on collision).

Gameplay Pickups
----------------
- Snake mode.
- Resurrect dead tanks?
- Grid mode (grid is overlaid on the level, tanks jump to adjacent grid squares
  when moving).
- Team mode (each player is assigned a random partner (i.e. 2 teams); their
  health is linked => when one is killed the other is too) (does that even
  work?).


****Done****
------------

Primary Shot Pickups
--------------------
- Fire multiple shots:
	- 3 forward.
	- 4 cardinal directions.
	- 8 octagon.
- Explode into 8 minor shots.
- Retaliating walls.
- Bounce off walls.
- Increase fire rate.
- Sine shots (tadpole shots).
- Spiral shots.
- Shots collect pickups.
- Homing shots.
- Shockwave.
- Shots trigger mines.
- Zombie bullets (create a zombie on death; zombies move towards nearest tank).
- Bullets which drop mines on death.

Secondary Shot Pickups
----------------------
- Decrease charge time.
- Diarrhea shots (i.e. tanks constantly fire secondary shots w/no input from
  player).
- Walls.
- Null field.
- Speed field.
- Slow field.
- Healing field.
- Incendiary field (explodes when a shot hits it).
- Turbo (speeds the tank forward in their current direction).
- Swap tank positions (each tank takes another's position).
- Bees.
- Camouflage mines (mines look like pickups).
- Colour barriers (puddles which only let same-coloured collidables pass;
  colour determined by the mine's colour).
- Turret mines.
- Zombie spawner mines.

Minor Shot Pickups
------------------
- Recursive shot properties (minor shots take the properties of the shot
  originally fired by the tank).

Tank Pickups
------------
- Regenerating health.
- Increase speed.
- Pinball mode (bounce off walls).
- Giant tanks.
- Bullets heal.
- Kamikaze mode (explode on contact with other tanks).

Gameplay Pickups
----------------
- Turn-based mode.
