Books: Fix backwards compatibility issues

Commit c68b8274 prevented books from
being copied in the crafting grid, and made it so that old books, though
seemingly successfully transferred to the new format, could not be written
to as the old data still persisted.

mods/default/craftitems.lua

@@ -71,6 +71,7 @@ local function book_on_use(itemstack, user)
 	end
 
 	minetest.show_formspec(player_name, "default:book", formspec)
+	return itemstack
 end
 
 minetest.register_on_player_receive_fields(function(player, formname, fields)
@@ -133,11 +134,11 @@ minetest.register_on_player_receive_fields(function(player, formname, fields)
 			end
 		end
 
-		local data_str = minetest.serialize(data)
-		stack:set_metadata(data_str)
-		book_on_use(stack, player)
+		stack:get_meta():from_table(data)
+		stack = book_on_use(stack, player)
 	end
 
+	-- Update stack
 	player:set_wielded_item(stack)
 end)
 
@@ -178,9 +179,9 @@ minetest.register_on_craft(function(itemstack, player, old_craft_grid, craft_inv
 	if not original then
 		return
 	end
-	local copymeta = original:get_metadata()
+	local copymeta = original:get_meta():to_table()
 	-- copy of the book held by player's mouse cursor
-	itemstack:set_metadata(copymeta)
+	itemstack:get_meta():from_table(copymeta)
 	-- put the book with metadata back in the craft grid
 	craft_inv:set_stack("craft", index, original)
 end)