Feature Request: Add summary output of var_selection

[mtnbikerjoshua]

Currently, an object of class var_selection prints as a nice table, but it contains much more information. It would be useful to add a summary.var_selection method to show a little more info. It could also be useful to have an autoplot.var_selection method that returns plots of the lambda values for the shrinkage methods and plots of number of variables against the stepwise metric.