format
A data.frame object with two columns. First column contains date id, and the second the realized volatility for S&P500 index.source
http://realized.oxford-man.ox.ac.uk/media/1366/oxfordmanrealizedvolatilityindices.zip{Heber,
Gerd, Asger Lunde, Neil Shephard and Kevin Sheppard (2009)
"Oxford-Man Institute's realized library", Oxford-Man
Institute, University of Oxfors}