A fastest mirror selector for apt-fast. Currently only works on Debian

To fetch the fastest mirrors and add the 10 fastest to the `MIRRORS` variable in `/etc/apt-fast.conf`, run:

sudo python3 af-mirrors.py

The fastest mirror is also added to `/etc/apt/sources.list.d/sources_<repo>.list`.

sudo add-apt-repository ppa:apt-fast/stable
sudo apt-get update
sudo apt-get install apt-fast

To ensure the script functions as intended, install `lsb-release`, `netselect-apt`, and `netselect`:

sudo apt-fast install lsb-release netselect-apt netselect

`netselect` and `netselect-apt` are not available in the Ubuntu repositories by default. They can be installed by downloading the Debian packages and installing them manually:

wget http://ftp.debian.org/debian/pool/main/n/netselect/netselect_0.3.ds1-30.1_amd64.deb
wget http://ftp.debian.org/debian/pool/main/n/netselect/netselect-apt_0.3.ds1-30.1_all.deb

sudo dpkg -i netselect_0.3.ds1-30.1_amd64.deb
sudo dpkg -i netselect-apt_0.3.ds1-30.1_all.deb