[Feature request] Add ability to automatically simplify mixed models following Singman and Kellen (2019)

[Joao-O-Santos]

Dear Prof. Singmann,

Thank you

Thank you so much for creating afex! afex greatly simplifies my analysis and my teaching (that I've used to spread the word about your package and model building approach).

Thank you, and Prof. Kellen, for outlining the approach to mixed model building that finally made mixed models "click" to me, and that makes more sense to me given the psychological data analysis tradition.

Feature request

Given the detailed and clear approach you outlined with Prof. Kellen, (students frequently ask and) I've been wondering if it would be possible to teach afex to follow it. The advantage is not only the time saved but also preventing human error in following the steps you outlined.

Related package

The buildmer package does some automatic selection for lmer fitted models, but if I understand correctly, it changes the fixed effect structure and doesn't follow your approach.

Next steps?

When and if you find the time, please let me know if you find value in this feature and what I could do to help in its implementation.

Sincerely, João (John)