Initialized Book and Borrower, implemneted Library add_book and list_book methods
Updated Borrower initialization, implemented borrowed_books, name, and borrowed_books_count
Updated Library's borrowed_book to be hash
Initial functionality achieved. Library.chechk_out working
Updated main to test out the Library's check_in method
Updated Library various list book methods. Updated Library check_in method. Updated borrower method to allow decrementing checked out book count.
Updated documentation for Library, Borrower, and Book