Gyroscopic Rings Generator

This is a parametric version of the excellent Gyroscopic Keyring by
**gianfranco** found here: https://www.thingiverse.com/thing:1307100

Thanks gianfranco!

I wanted to be able to experiment with the number of rings, spacing between
rings, sizes, etc. so created this parametric version that allows the
customizer in OpenSCAD or the Thingiverse customizer to be used to alter the
model.

**Note** that you are encouraged to make your own customized version since I'm only providing one simple STL as proof of concept. I'll add more STLs of different variations if there is a need.

The default settings will generate a model that is almost identical to the one above, but using the customizer, either the one built into OpenSCAD from the latest development snapshot versions (these are very stable), or the Thingiverse one, you can modify many settings to generate your own version by:
* changing the inner ring size and central hole size - this affects the final gyro size
* setting t