Parametric Shaft Collar - Improved

This is an improved version of timschmidt's parametric shaft collar at http://www.thingiverse.com/thing:2454.

In my original version, a tolerance parameter was added that can be used to improve the final size of the holes for the shaft, the clamping screw, and the trapped nut. The amount of material to be placed in front of the trapped nut was a new parameter. Finally, a parameter is provided for specifying the number of facets to be used.

Rev A is mostly a refinement in how openSCAD