Get GPIO working on RPi to drive the stepper.

Two things learned this evening.
(1) Run the server as root, or else no GPIO for you!
      $ sudo su -
      % cd ~pi/CylindricalPrinter/software
      % source setup.sh
      % ./printer.py
(2) In order to pip-install RPi.GPIO, you need to first
    sudo apt-get install python-dev