fixed yahoo.finance.stocks.xml

The table was broken for some reason and only return the stock symbol in the results. Submitting fixes to address to problems and also added a few more stock summary information. See these dev forum threads for more details:

https://developer.yahoo.com/forum/YQL/Issues-when-using-Yahoo-Finance-tables/1408006870634-e1c10978-2638-4da4-9edb-746dbd1c1d1b
https://developer.yahoo.com/forum/YQL/yahoo-finance-stocks-returns-result-with-only-the/1408086742121-c49c830b-a349-4482-81a9-3068dba95b29