Tasks
Library

    Book: title, author
    Order: book, reader, date
    Reader: name, email, city, street, house
    Author: name, biography
    Library: books, orders, readers, authors

Write program that determines:

    Who often takes the book
    What is the most popular book
    How many people ordered one of the three most popular books
    Save all Library data to file(s)
    Get all Library data from file(s)