init commit forecast engineer ...

[tommylees112]

Create an engineer for specifically dealing with forecast data:

This takes the forecast variables for the target timestep and the target variables for all previous timesteps (not the target timestep).

This produces a dataset:

        t-3  t-2  t-1  t=0   |  y (t=0)
        --------------------------------
        X Y  X Y  X Y  fcast |  Y
                             |  Y