Added Optional Support For List Of Dictionaries for get_historical_prices

Hi Corey,

Thanks a lot for sharing your module . I have added  a optional argument to get_historical_prices() to allow for results to be returned as a list of dictionaries without breaking the current module for other users.

Could you merge into your module and push update to  PyPi when you have the time ?

```
>>> list_dict = ystockquote.get_historical_prices('GOOG', '2013-01-03', '2013-01-08',list_dicts=True)
>>> just_list = ystockquote.get_historical_prices('GOOG', '2013-01-03', '2013-01-08')
>>> just_list
[['Date', 'Open', 'High', 'Low', 'Close', 'Volume', 'Adj Close'], ['2013-01-08', '735.54', '736.30', '724.43', '733.30', '1676100', '733.30'], ['2013-01-07', '735.45', '739.38', '730.58', '734.75', '1655700', '734.75'], ['2013-01-04', '729.34', '741.47', '727.68', '737.97', '2763500', '737.97'], ['2013-01-03', '724.93', '731.93', '720.72', '723.67', '2318200', '723.67']]
>>> list_dict
[{'2013-01-08': {'Volume': '1676100', 'Adj Close': '733.30', 'High': '736.30', 'Low': '724.43', 'Close': '733.30', 'Open': '735.54'}}, {'2013-01-07': {'Volume': '1655700', 'Adj Close': '734.75', 'High': '739.38', 'Low': '730.58', 'Close': '734.75', 'Open': '735.45'}}, {'2013-01-04': {'Volume': '2763500', 'Adj Close': '737.97', 'High': '741.47', 'Low': '727.68', 'Close': '737.97', 'Open': '729.34'}}, {'2013-01-03': {'Volume': '2318200', 'Adj Close': '723.67', 'High': '731.93', 'Low': '720.72', 'Close': '723.67', 'Open': '724.93'}}]
>>> import pprint
>>> pprint.pprint(list_dict)
[{'2013-01-08': {'Adj Close': '733.30',
                 'Close': '733.30',
                 'High': '736.30',
                 'Low': '724.43',
                 'Open': '735.54',
                 'Volume': '1676100'}},
 {'2013-01-07': {'Adj Close': '734.75',
                 'Close': '734.75',
                 'High': '739.38',
                 'Low': '730.58',
                 'Open': '735.45',
                 'Volume': '1655700'}},
 {'2013-01-04': {'Adj Close': '737.97',
                 'Close': '737.97',
                 'High': '741.47',
                 'Low': '727.68',
                 'Open': '729.34',
                 'Volume': '2763500'}},
 {'2013-01-03': {'Adj Close': '723.67',
                 'Close': '723.67',
                 'High': '731.93',
                 'Low': '720.72',
                 'Open': '724.93',
                 'Volume': '2318200'}}]
```