Get All Books API #13
This PR implements the getAllBooks function that can be used to get summary information about all the books, in order to display them on the main page.
I'm not sure why I waited so long to create this PR, but I suspect that we were blocked by #11 (which has now been merged).
Deleting a branch is permanent. Although the deleted branch may continue to exist for a short time before it actually gets removed, it CANNOT be undone in most cases. Continue?