Minimal Non-geared Mendel Extruder

Based on http://www.thingiverse.com/thing:1524

I bootstrapped my mendel using a plastruder - which I miss treated and killed. While it was dying, I edited the mendel extruder block to use as little plastic as possible - here is the result.

It has been tested, and it works. But, it is a pain to set the tension - so if you don't need a minimal extruder block: don't print it.

(It is much smaller than both Wade's and Adrian's geared extruders as well)