Add reflector mirror ranking support.

It would be nice if `archdi` has a feature to rank mirrors using `reflector`.

After all, the `pacman` hook for `reflector` is a bit complicated, and some people are just too lazy to run `reflector` every week, you know.

Install `reflector`:
```
sudo pacman -S reflector
```
Archwiki page on `reflector`:

[https://wiki.archlinux.org/index.php/reflector]()