Geared extruder v.3

This is an improved version of the Geared Extruder v.2 (http://www.thingiverse.com/thing:933829), added spring adjustable tensioner and stepper position adjustment (only needed for easier maintenance and if your gears have rough surface and cannot fit nicely).

This version was not tested yet, if you are looking for 100% proven solution then stick to the previous edition.