Organization; Whitespace

I moved some files around for organization. I wasn't sure where to put the files I did not move that are directly in the `lib/` directory:

```
lib/
  application.rb
  authenticator.rb
  category.rb
  inventory.rb
  order_book.rb
  role.rb
```

Naming is important in programming, and even more so in learning. I wasn't absolutely sure what to call each of these. What would you call them?