Improve the docs

[andrewdavidmackenzie]

Improve overall docs - I need to learn how to properly document modules, structs, traits and functions in rust following the bets guidelines.

A couple of functions need descriptions or links to the apple docs on the subject

[andrewdavidmackenzie]

Use mdbook, create a SUMMARY.md and book.toml in the project root, include README.md and link to the indexes created for each bin/lib module by cargo doc