Villager Trading Mechanism Optimization

When you enter the game with this mod, you may find that the villagers' output slot has added another slot in.It is called "the bottle slot".Its function is to give you a "leveling bottle" to upgrade villagers to the next level(For example, Novice --> Apprentice, Expert --> Master, etc.) when you traded within a "bottle trade offer", which is highlighted with light yellow in the villager's tooltip.When you trade within this kind of offer,you may not be able to click your left mouse button at once to grab the normal output item or the bottle out.Instead, you may shift click the normal output item or the bottle to move both of them into your inventory, provided that you have enough space to put them in.One bottle can only upgrade a villager with specific profession and specific level(like Librarian at Journeyman), which is declared in the description of the item.When you hold the bottle in your mainhand, or hold the bottle in your off hand and a unusable item(like diamond sword, totem of undying, etc.) in your main hand, you can use the bottle to the villager by right clicking once to upgrade him.The leveling amount is mentioned above.