Add: get and set serializer function

colddb.lua

@@ -64,7 +64,7 @@ function colddb.Colddb(dir)
 		use_async = value
 	end
 	
-	self.get_serializer_type = function(value)
+	self.get_serializer_type = function()
 		return serializer_type
 	end
 	
@@ -75,6 +75,10 @@ function colddb.Colddb(dir)
 			deserializer = minetest.deserialize
 		end
 	end
+
+	self.get_serializer = function()
+		return serializer, deserializer
+	end
 	
 	local function file_exists(name)
 		local f = io.open(string.format("%s/%s.cold", directory, name), "r")