Finite differences is double-defined in utilities

[pavelkomarov]

I tried to remove it and import instead from the actual finite difference code, but this causes a circular dependency. Something is fishy about the way this is structured. It's possible that simulations need to live somewhere that isn't the utilities folder. I'm giving it some thought.

[pavelkomarov]

Okay, I think we can solve the problem by clearing the contents of pynumdiff/utils/__init__.py, because we can already import utility and simulate and evaluate without making entries for them in here. You really only need entries in an __init__.py if you're aliasing somehow. Really the dependency chain goes simulate -> FD -> utility, so we just need to break the co-importing of simulation and utilities.