Added not-open-when-invalid option support in buy more menu settings in config.yml file. If there is only a purchase button in the buy more menu and the product is not purchasable (meaning there is no buy price), then we consider this buy more menu to be invalid and cannot be opened, and the same applies to sell.
Updated example files for example shop and example daily shop, if you already generated them, try delete your UltiamteShop configs and they will auto regenerate new example files.
Added ShopHelper class to help developer quickly get target product or buy/sell price from ItemStack object.
Added /shop search command.
This command currently only mentions text output of target product information, and in future versions it will mention GUI display of search results. Thanks to this API improvement, we plan to add the instruction/shop sellhand in the future.