Parametric Filament Hub

I remixed the original to parameterize the dimensions and put the sub-assemblies into modules in OpenSCAD. None of that is visible in the STL, of course.

I also made the default bore compatible with a skate bearing, and changed the shape of the material reserve areas from circles to wedges in between the hooks, which should save a bit more plastic without changing the functionality much. Hopefully.

**UPDATE:** I have printed this, and made adjustments necessary to get everything to fit, using a Hatchbox spool and some skate bearings I happened to have. Things fit pretty snugly, which is good IMO.