WIP: refactoring of https://wiki.debian.org/AptConf and other apt configuration pages


Apt is configured by several resources, including:

=== apt.conf.d

Apt accepts configuratino files (without extension) in /etc/apt/apt.conf.d/. These are processed by Apt in numeric/alphabetical order. /etc/apt/apt.conf is also valid but deprecated.

These files can contain various directives: