Mike Mayer and Anuj Jhunjhunwala stock app

The app doesn't quite debit/credit cash properly when buying/selling stock. Other functionality seems to work, though parts are messy (ie, the functionality to add up a portfolio's value would definitely need to be refactored into something more efficient). The main.rb file in the "classes" folder is the main file to run, with the others feeding in. Trade.rb was not used and could probably be deleted, though I kept it around in case we decide to use it at some point. 

-Anuj