Fama French Factors keys should be descriptive

[MichaelWS]

web.DataReader('F-F_Momentum_Factor', 'famafrench') returns a dict of 1,2 pointing to monthly, annual data.
I believe the dicts should indicate about the data.
pandas-dev/pandas#8842

[jreback]

can u add a link to the oandad issue as well thxs

[davidastephens]

I believe this was fixed with #56, please reopen if not.