Parametric Pulley Library - Retainer improved

This is a remix of [TNS](https://www.thingiverse.com/TNS) [remix](https://www.thingiverse.com/thing:2136539) of [droftarts](https://www.thingiverse.com/droftarts) [thing](https://www.thingiverse.com/thing:16627)

Take care: This will only take effect if the pulleys diameter is lower than the bases diameter. The pink pulley in the first picture for example will be drawn in the conventional way.

I improved the generation of the belt retainer. The chamfer for the transition from the teeths to the retainer will get a fix angle of 45 degrees (better for printing without support). If the so from the hight resulting diameter of the retainer is lower than the bases diameter the generation will be done like in the original script. If the diameter will be higher the chamfer stops at the bases diameter and the edge will continue vertical from there. See attached picture as example for this case. Additionally I made the precision for the circle generation customizable. The original value was