User.java is added with basic / expecting data and functionality

Main.java
- removed redundant newBook()

Book.java
- Added a condition if the book is not overdue

BookFactory.java
- Removed empty newBook()
- Added “throw new NullPointerException()” on both getBook() if Book is
not found

BookFactory.java
- newBook() now returns the new ‘Book’ created instead of ‘void’
- if getBook() failed, it now returns an empty ‘Book’

Book.java
- overdueFine(int[]) is now rewritten

Book.java
- Added comments for Book.java
- Added getter for id
- Added setter for title
- Removed the need of ‘status’ in constructor
- overdueFine(int[]) not commented as it needs to be updated

BookFactory.java
- need for (String status) is removed

Book.java
- Added String type ‘title’
- Added new constructor to include ’title’

Main.java
- Added Main.java (mostly still empty)

BookFactory.java
- Added newBook(String) for the new ‘title’ implementation
- Added getBook(String) to look through ArrayList for Book with the
given ‘title’
- Error handling for both getBook still needs more work

BookFactory is now implemented to handle all the books.

Added some simple functions including rent() and calculating
overdueFine()