Bug: no way to call hero inside of item scripts

Talking with Max on discord, we realized that there's no way to tell inside of an item's on_using() event what hero called that event. Max seemed to remember that event being changed in 2.0 to pass a hero object, but it doesn't take any values, so this may be an oversight that affects anyone trying to make multiplayer quests. Might be worth checking other events to see if they should also be changed to require the hero being given them as an argument.