Combine any written book with an empty book to copy it. The
copy is in player hands when using, and the original is put
back on the crafting grid and can be directly copied again.
All ownership and metadata is retained, so the copy of the book
is as writable as the original is, or isn't.
Since written books are quite different from empty books, the
visual clue that they are different items is really needed in-game.
I've added a "clasp" or "belt-with-buckle" like element to the
png from default_book, keeping them very similar but also
immediately recgnizably different.
I added the new texture to blockmen's license list since it's
obviously derivative of his work.
The PNG was run through a minimizer/optimizer to save space.
