add class() for easy definition of classes

code/entities/decoration.lua

@@ -1,8 +1,8 @@
-Decoration = {}
-Decoration.type = "Decoration"
-Decoration.supertype = Entity.type
-Decoration.display = Animation:new(animation.particle.simple)
-setmetatable(Decoration, Entity)
+Decoration = class(Entity, {
+	type = "Decoration",
+	supertype = Entity.type,
+	display = Animation:new(animation.particle.simple),
+})
 
 function Decoration:new(x,y,animation,light_data)
 	local o = Entity:new(x,y)
@@ -22,7 +22,6 @@ function Decoration:new(x,y,animation,light_data)
 	o:id()
 
 	setmetatable(o, self)
-	self.__index = self
 	return o
 end