Flatten import structure

[magnusuMET]

Removes visible modules (leaving types) to make the documentation clearer.

This is a breaking change and may require crate users to update their code

[lnicola]

An alternative here, which might be preferred, is to keep using the nested structure, but make it private and add re-exports. Probably doesn't matter too much though.

[magnusuMET]

@lnicola not entriely sure I understand wat you are suggesting. This change does make most modules private and only changes the public API by moving items to the top-level.

[lnicola]

wat you are suggesting

Exactly what you did, sorry :pensive:.

[magnusuMET]

We have the same idea for how to structure this crate, which is great! 🙂