Prompt the user to make either a bird, cat, or fish

Project Goals
- Continued use of makefiles
- Continued use of class building skills
- Practice with new Abstract Base Class skills
- Provide practice with new virtual functions skills

 Program
This program will prompt the user to make either a bird, cat, or fish.
These three classes will inherit from the Abstract Base Class - Pet.
After creating the Pet objects, the user will be prompted to feed the pet
by accessing it's eat() virtual function.