Enlarged Rostock Idler End V1.2 for 12mm Smooth Rod

Rostock Motor End originally from Jcrocholl

- V1      - Thanks to the excellent parametric setup         no change ere necessary for this file the change         made to bracket.scad where directely useable  - V1.1       - Added stiffeners to better carry the load of the pulley        I hesitated with the boxed concept but I guess this will keep        the pulley accessible        The switch holder is not usefull anymore  - V1.2       - Enlarged the walls around the rods to prevent cracking      - Reduced lower stiffeners for better end stop integration