This is an updated version of Pablo Bianciotto's (akhanubis) script so it works again after SteamGift changes.
The original author's website is dead and as far as I can tell he's not been around SteamGifts or Greasy Fork for a while hence my update. Should he come back then I'll gladly return maintaining the script back to him.
The original can be found here: https://greasyfork.org/en/scripts/14840-steamgifts-ga-creator