External spool holder

Allows a large filament spool to be used on a Fabtotum fabricator. This is a respin of shomar's excellent one at http://www.thingiverse.com/thing:649462, but I had some parts from an old inkjet printer on hand, so I used one of the rods from that printer which are smaller than the one that shomar designed for.

Also includes the scad files to allow you to specify the diameter of any rod you might have on hand.