Parametric Cable holder

When I was searching it seemed like I could get nice rounded cable holders, but as STL only files, or parametric options which didn't look the way I wanted. [This option](https://www.thingiverse.com/thing:4172528) was very close, but doesn't allow tweaking of the dimensions.

I used [Pyopen's cable holder](https://www.thingiverse.com/thing:96000) to help figure out the dimensions.

The code is all new. The OpenSCAD customizer will allow you to set -

- Number of cables
- Diameter of the holder
- Size of the top opening
- Size of the opening at the bottom
- Height of the bottom of the opening

If there is interest I may allow you to control the distance between the cables when you have more than one.


##Edit on 2022-Jan-3
Fixed reported problem for single cable version

### 2nd Edit
Cleaned up some code and moved to using "hull()" for the overall shape

##Edit on 2022-Jan-4
Didn't realize the highlight on the cutting piece would come through on the customize