snapshot prior to removal of recipes code

parsnip will be agnostic to recipes after this release of the master branch.

The reason is that the recipe would have to be bound to the fitted model.

That's a bad idea because future code should be able to train a recipe and then use it across many different models (or sub-models). The version is this release is tagged because the existing code can be recycled into the other packages that will need to use recipes for different models.

First prototype version

original_prototype

Updated tests