Refactor

- `Homesick` is now a module, not a class.
- The original Thor-related code in `Homesick` is now in the `Homesick::CLI` class.
- `autoload` calls have been removed, since it was an easy fix after ensuring that `Homesick` was a module (fixes #108).
- `Actions` has now been split up into two modules: `Actions::FileActions` and `Actions::GitActions`.