Generators should be extensible

[landon-buttars-wgu]

The current approach to generators is very black box for anyone consuming them. They make changes and cannot be affected from the function calling them.

For example, if I were to have a generator that were to call another generator I would want to be able to affect and modify some of the steps and variables that the generator may execute. Currently this is achieved through parameterization for the variables but it is not possible to affect the actual steps it takes.

I propose creating a way to register changes in a way that is hookable. That way if I need to change a small subset of functionality on an otherwise complex generator I'm only needing to change the single step.

The core idea being that generators should be extensible by their very nature.