So that convention also applies to plain python files? I thought it was just cython files.

I think unwrap.py -> _unwrap.py is unfortunate, as that gives the impression that the file contains private functions only (that's how I would approach a file with a leading-underscore name, anyway), when in fact it defines a public function (I'm aware of `unwrap()` being exported also on the `exposure` package level).

I'm not planning to merge the 2D and 3D cython extensions for the reasons explained below. If we really, really need to, I will need help debugging the segfaults. As the cython files are named now, the names of the modules are not equal to the name of the functions, so no renaming should be necessary here, right?