Allow the preprompts to be overridden for a certain project

[brainshower]

I am planning to experiment with some project-generations that are not necessarily written in python, or even a language that utilizes classes. So, instead of overwriting the current preprompts, I think it's useful to enable overriding one or more preprompts on a project-by-project basis.

For instance, in your project directory, you'll have the file "prompt" (was main_prompt), and possibly an optional preprompts/ directory with any overridden files. If that preprompts/ project directory doesn't exist (or is empty), nothing changes. Otherwise, any text file of the same name as the one in the main preprompts/ directory will be used during generation.

Thoughts? Is there currently another way to accomplish this?