Get rid of deprecated metadata (#628)

The deprecated metadata gets converted to a proper ItemStackMetaRef.
All keys stay the same except for:
- Cans that use `can_level` now, since they didn't store a serialized table in the metadata before.
- `charge` which is now `technic:charge`, since any item (also from other mods) may have a technic charge which can cause compatibility problems.

Backwards compatibility is kept but going back to older `technic` versions might result in misbehaving circuits.

technic/tools/sonic_screwdriver.lua

@@ -41,8 +41,9 @@ local function screwdriver_handler(itemstack, user, pointed_thing, mode)
 	-- contrary to the default screwdriver, do not check for can_dig, to allow rotating machines with CLU's in them
 	-- this is consistent with the previous sonic screwdriver
 
-	local meta1 = minetest.deserialize(itemstack:get_metadata())
-	if not meta1 or not meta1.charge or meta1.charge < 100 then
+	local meta = technic.get_stack_meta(itemstack)
+	local charge = meta:get_int("technic:charge")
+	if charge < 100 then
 		return
 	end
 
@@ -64,9 +65,9 @@ local function screwdriver_handler(itemstack, user, pointed_thing, mode)
 	minetest.swap_node(pos, node)
 
 	if not technic.creative_mode then
-		meta1.charge = meta1.charge - 100
-		itemstack:set_metadata(minetest.serialize(meta1))
-		technic.set_RE_wear(itemstack, meta1.charge, sonic_screwdriver_max_charge)
+		charge = charge - 100
+		meta:set_int("technic:charge", charge)
+		technic.set_RE_wear(itemstack, charge, sonic_screwdriver_max_charge)
 	end
 
 	return itemstack