Improve clarity of code organization

[alice-i-cecile]

As a new reader, it's quite challenging to follow exactly how the code is organized and where to look. From my perspective, I think there are three sources of this:

1. Very flat code organizational structure.
2. main.rs doesn't have strong organizational principles.
3. Examples and introductory documentation are largely missing.

This isn't a huge problem at this stage, but will matter a lot more as you intend to share the code more widely :)