10mm Lighting System v2

[2019-08-30 22:00-5 Updated from an earlier version]

## Overview

This is a somewhat generalized lighting-bracket system consisting of 10mm square bars
connected by various kinds of joints and fixtures. The joints and fixtures include the
following:

- a standard 270 degree Radial Joint set with a male end, and a female end
- a Universal Joint with a 360 degree rotating "cap" and a female radial end
- a Ball Socket End that can join a 10mm rod to a 20mm ball making a joint
- an exa