T5 & XL Parametric Pulley

>**Update:** An updated version of this file, with a bigger variety and more accurate tooth profiles, is available here: http://www.thingiverse.com/thing:16627

One of the things I've been trying to do is print a pulley with a captive nyloc nut. However, the pulleys in PrusaJr's and Greg Frost's github pages, and the ones on thingiverse, all have some problems. Mostly it's that they are not parametric, or not openscad, or just stl, or rely on other files (Prusa's and Greg's) for some reason. S