Wandering trader buff

Allow you to trade creaking hearts and emeralds for mending books, rather than trading with villagers. Advantages: - Encourages exploration - Makes silk touch useful - Could still cost emeralds to make it harder and more fun to get without requiring transporting a villager to a swamp - Wandering traders are now useful - Encourages going to the pale garden during nighttime in an attempt to gain endgame loot - More endgame content