Mad Science filament guides for printrbot simple

This helps guide the filament, adds a surprising amount of rigidity to the otherwise not-so-rigid z-rods, and looks great doing it.

It prints fine for me without support material. I stuck my own support on in the form of those circle things that keep the spheres from rolling away before they join the rest. It trims off easy.

I included two versions, one uncorrected, and one corrected for the tendency of these printers to squash horizontal holes. Print the clamp_test.stl first to see whi