MakingLibrarySoftware4

1. Implement the methods for add_book and remove_book.

2. Now, try to write methods for find_book and get_all_books.

3. Download menu.py, examine the Menu class, a subclass of cmd and see how it separates the user interface (asking the user about books) from the data access (the code that stores the books). This separation will become more important if we make a web interface, GUI, etc.