Description

Removes deprecated code and updates docs with FormulaicTransformer.

Checklist:

[X] My code follows the style guidelines (flake8)
[ ] I have commented my code, particularly in hard-to-understand areas
[X] I have made corresponding changes to the documentation (also to the readme.md)
[ ] I have added tests that prove my fix is effective or that my feature works
[ ] I have added tests to check whether the new feature adheres to the sklearn convention
[X] New and existing unit tests pass locally with my changes