prusa i3 Zonestar p802/Anet A8 z axis upgrade V2

evolution of the previous version ( http://www.thingiverse.com/thing:1205037 )
but with the following improvements.
* 2:1 step down gear ratio for z stepper (2x torque to compensate for 1 less motor)
* More adjust-ability in belt tension (3 motor mount positions, more range in fixed idlers and more adjustment for screw adjustable idler)
* M8 rods to tie down top caps and the ability to triangulate to reduce X wobble.

For reference:
The M8 bolts joining the M8 connector blocks are M8x40.