Save residuals after OLS fit

[smmaurer]

From @cvanoli:

Found a better way actually, since the fit function in the Regression Model in urbansim_templates uses the model_fit from urbansim.models, which at the same time, uses the statsmodels.regression.linear_model.OLSResults we can get the residuals from the fit object like the urbansim.models does here : https://github.com/UDST/urbansim/blob/master/urbansim/models/regression.py#L344.

So, I would suggest the following two lines to solve this:

1. Add here https://github.com/UDST/urbansim_templates/blob/master/urbansim_templates/models/regression.py#L104 a self.residuals = None
2. In the fit function after the fitted parameters: https://github.com/UDST/urbansim_templates/blob/master/urbansim_templates/models/regression.py#L192
   add self.residuals = results.resid

So in estimation, after you fit the model you can call the residuals as m.residuals