Getting residuals

[spsanderson]

I think it would be great to have an extractor that would get the residuals of the model. So far I have an implementation of this for regression models which can be seen here:

#187

This only covers regression models and I think should be part of another function that will check for residuals based on the model being either regression or classification.

[spsanderson]

I added an extractor to get the regression residuals but need one for classification models.

[spsanderson]

In issue #198 I added the parameter .pivot_long to put the residuals in long format which is good for plotting in ggplot2