Add z-axis mounts with +5mm between motor and smooth bar, for lead screw

http://www.thingiverse.com/thing:289720
My config
Modify z-axis for bigger distance between motor and smooth rods (for lead screw)
Modify z-axis to support option for top bearing for lead screw
Typo
Add high-res mod of involute gear lib

http://www.thingiverse.com/thing:97377
Lots of mods to herringbone extruder gears, including tapped nut mount for small gear.