Grind enchantments adds a few new features to the grindstone.
Disenchant to book
You can put an enchanted item and a book into the grindstone, and you will get the enchantments onto the book (and your unenchanted item back).
Move enchantments between books
If you put an enchanted book into the top slot and an empty (or also already enchanted) book into the bottom slot of the grindstone, the enchantment at the top of the first book will be put onto the other book.
This is useful if you have a book that has enchantments for different types of items (for example, a book with Efficiency and Protection), so you can separate them.
