googleTrends addition

Let me know if there are some changes that should be done, I am testing this my self now and it at least has run two days in a row for me.
I would rather return None explicitly from your function ```__readXML()```. See [StackOverflow](http://stackoverflow.com/questions/15300550/python-return-return-none-and-no-return-at-all). Although, ```return``` does in fact returns None, but it's not that indicative, that the value will be used later.