consistently use the same summary functions

[njtierney]

It would be great if all of the summary type functions didn't repeat hand-written code or repeat other chunks of code.

So, ideally I should be using the recently added summary_user_cov and n_relocated and augment_ functions inside the maxcovr functions, either as an extraction type method, or something else.

Also keep in mind that there should be a broom::tidy-like function, as well as something like a rmse or other summary that works with map2.

So I should be able to do something like map2(lm_train, test, rmse).

So instead I guess that would be: map2(mc_model_train, test, summary_user_cov).