Moved BitmapData and RenderTexture into the textures folder for now.
All Game Objects now have their own sub-folder, with their Factory and renderer functions alongside them, plus any other files they need.
New Factory class added. Currently hooked into `game.factory` for testing, but will swap to `game.add` when complete.
Weapon.fire has two new arguments: `offsetX` and `offsetY`. If the bullet is fired from a tracked Sprite or Pointer, or the `from` argument is set, this applies a horizontal and vertical offset from the launch position.
Weapon.fireOffset attempts to fire a single Bullet from a tracked Sprite or Pointer, but applies an offset to the position first. This is a shorter form of calling `Weapon.fire` and passing in the offset arguments.
Weapon.fireMany attempts to fire multiple bullets from the positions defined in the given array. If you provide a `from` argument, or if there is a tracked Sprite or Pointer, then the positions are treated as __offsets__ from the given objects position. If `from` is undefined, and there is no tracked object, then the bullets are fired from the given positions, as they exist in the world.
