Added more OOP files

- Went over how the parent:: special name works. you can use this to
reference parent class functions inside of class functions with the same
name
- Went over constructor. Basically the __constructor method will fire
every time a new object is instantiated
- Discussed cloning objects. This is great because object are always
references in OOP so the clone modifiers allows to create a brand new
object without change the original
- Finally went over references and clones