use class() in more places

code/collision.lua

@@ -1,4 +1,4 @@
-Collision = {}
+Collision = class()
 
 LoadedObjects.Collisions = {}
 LoadedObjects.Platforms = {}
@@ -48,7 +48,6 @@ function Collision:new(ox,oy,tx,ty)
 	end
 
 	setmetatable(o, self)
-	self.__index = self
 
 	return o
 end