Add "has optional year-published and edition parameters" test.
Rewrite invalid class names.
Add year_published and edition class variables.  Changed the logic of
how Library assigns an ID to a book to be explicit instead of at
instance.
Add Extentions section to README.md
Add "allows books to be rated with an optional text review" test.
Creates two new books and has a Borrower give the first book a rating
and a short review and the second book just a rating.
Pass the "allows books to be rated with an optional text review" test.
Update README.md to include a newly checkoff extension.