It's much better these days!

    $ cd redox
    $ git grep "unsafe" kernel/ | wc -l
    67
    $ loc kernel/
    --------------------------------------------------------------------------------
     Language             Files        Lines        Blank      Comment         Code
    --------------------------------------------------------------------------------
     Rust                    42         5743          894          366         4483

The changes include:
- Editing for flow and understandability.
- Unifying how links are included in the source files.
- Adding an `About this Book` page to the introduction.
- Adding a few examples or new pieces of information I felt were
  lacking when I read the book.
- Unifying 'user space' and 'kernel space' spelling.
- Added myself to the authors list in `overview/welcome.md`.