Allow time series of 3D vectors
We use Pandas to analyse flight data. Many of the recorded measurements are 3D vectors of double, e.g. position, velocity, acceleration. Currently I can only store scalars or objects in a time series. Scalars make the dataset very large, processing it is not very convenient.

I would like to be able to do:
df.velocity.norm().plot()

to plot the norm of the velocity vector that is stored in the data-frame. 

Currently I have to type:
pd.Series(np.sqrt(df.velocity_x**2 + df.velocity_y**2 + df.velocity_z**2)).plot()

which is not very convenient.
