Bonus effects

1. Detect bonus-platform collision

function collisions.resolve_collisions( ball, platform,
                                        walls, bricks, bonuses )
   .....
   collisions.platform_bonuses_collision( platform, bonuses, ball )
end

function collisions.platform_bonuses_collision( platform, bonuses, ball )
   local overlap
   local b = { x = platform.position.x,
               y = platform.position.y,
               width = platform.width,
               height = platform.height }
   for i, bonus in pairs( bonuses.current_level_bonuses ) do
      local a = { x = bonus.position.x,
                  y = bonus.position.y,
                  width = 2 * bonuses.radius,
                  height = 2 * bonuses.radius }      
      overlap = collisions.check_rectangles_overlap( a, b )
      if overlap then
         bonuses.bonus_collected( i, bonus, ball, platform )
      end
   end
end