Outlier-Robust Dose-Response PL models

[pzivich]

Is your feature request related to a problem? Please describe.

It is related to an analytic problem (not a software problem).

Describe the solution you'd like

Implement a robust version of the PL models, where the models are robust to response outliers.

Describe alternatives you've considered

NA

Additional context

This problem came up in discussion with people I've talked to. They were excited about the opportunity for PL models that are robust to the presence of outliers, since this is a common issue.