added order
- stocks can now be compared for equality stocks based on symbol
- stock.price now returns the most recent close
- now able to call .each directly on a watch_list
- watch_list.remove(positions) can now be used to prevent buying a stock more than once
an action can now be created from a string (e.g. "BUY" or "SELL")
yahoo finance lookup now automatically replaces spaces with dashes (e.g. "BRK A" -> "BRK-B")
refactored trading systems
updated gem version