Simple Belt Tensioner for Printrbot Jr -- GT2 belts

This is a simple belt tensioner made by 3d0g.

I've made the following changes:

Reworked slot and teeth to fit GT2 2mm pitch belt.
Added a third screw to clamp tighter around on belt.
Thickened sides a bit around nut.
Rounded the edges to the slot to make it easier to insert belt

When tightening, I found it kept wanting to pivot and not pull away from the printer body. I addressed that by adding nuts to the end of the screws for a more stable "foot" and pulling the loose cable end