GET /api/books should return the latest
booksDirectory variable
The route GET /api/books/:id should return the correct book object when requested
The route POST /api/books should append a book to the booksDirectory memory variable. It should also return the appended book object as JSON
The route PUT /api/books should try to find the passed book by "id". If the book is not found, return a status code of 404 with an appropriate message
On the route PUT /api/books if the book is found, it should replace all the undefined parameters. This means if only title is passed in the body, it should only update title and nothing else.
The route DELETE /api/books/:id should delete the book if present. Once the book is deleted, the call to GET /api/books/:id should return 404 too