VIX quandl data import

[miguelvm]

On march 26th 2007 VIX futures where rescaled as described in http://cfe.cboe.com/publish/CFEinfocirc/CFEIC07-003%20.pdf

Data imported from quandl before this date should be divided by 10 in order to backtest accurately.

[chrism2671]

Ah yes, this happens a bunch with historic data. I'll be rewriting this section so that data can be reformatted on the fly (currently it's reformatted on download, which is problematic in situations like these).