Configure APT for raspbian

NB.
Raspbian continues as a distro, but the packages it uses are just Jessie armhf ones

As from 22.Oct.2017 specific Raspbian packages will no longer be produced

If you want to continue to update as changes to the code are made
just substitute raspbian in the below stanza with jessie

If you have already installed raspbian packages and want to use Jessie,
purge them first and install anew.

1. Add Machinekit repository

sudo apt-key adv --keyserver hkp://keyserver.ubuntu.com:80 --recv 43DDF224
sudo sh -c \
  "echo 'deb http://deb.machinekit.io/debian {raspbian|jessie} main' > \
  /etc/apt/sources.list.d/machinekit.list"
sudo apt-get update