Request:Is it possible to add exponential, smallest extreme value, normal, logistic AFT models

[leavor]

Is it possible to add exponential, smallest extreme value, normal, logistic AFT models in later releases. Exponential distribution is a frequently used distribution type, and other distributions are used less often.

[CamDavidsonPilon]

@leavor this are possible to build quickly with the library: https://lifelines.readthedocs.io/en/latest/jupyter_notebooks/Custom%20Regression%20Models.html

There's an example of the Exponential dist there.

I chose not to include all these as they would confuse new users (too many options for models), so I kept the most popular ones (IMO).