Belted extruder gears for Greg's Wade / L3K and many more

UPDATE (06-FEB-2017): After a year of flawless work with the ABS Crown pulley I had some aluminum pulleys around and ended using an aluminum standard GT2/60T pulley with a GT2/16T pulley. Added a model for a manual handler fixed to the pulley with M3 screws. Torque of 1:3.75. 580 Steps for 16 microstepping pololus and standard 8mm hobbed bolt. No so cheap but more durable/precise. Used high torque 160mm S2M belts. Don't know why, but extrusion seems to be smoother now. I'll update this when I ha