Documentation should make types clearer when using non-default MatTypes

[rcurtin]

This is a follow-up to this discussion.

The LogisticRegression documentation in doc/user/methods/logistic_regression.md has a section on non-default MatTypes (render); however, the fact that the types of a number of methods are changed is not mentioned.

It's not clear yet what the best way to address this is, but I want to write this issue down so it doesn't get forgotten. All of the methods that have MatType as a template parameter (most of them) will need to be updated with whatever the strategy here is.