created the GrandParent class
Created the GreatGrandParent class
Modified the to_s method to show the class of the object
Added the option to add a GrandParent to the family tree
Added a method to show all objects of a given Class
Fixed error on initialize method where sons array was not properly intialized
Rewrote the get method so it gets works with blocks
Added the option to add a grandparent and set its own parents
Refactor code
Merge pull request #3 from OscarSwanros/feature/add-grand-parents

feature/add-grand-parents