Add renders for inserting the illumination wire

Based on the code provided by @julianstirling in #430 (closed), with some extra modifications to make it more realistic where the wire meets the cable.

• Adjust the flat_wire_points() function to allow the wires to be further apart and at a special orientation at a connector.
• Add renders in mount_illumination.scad for inserting the illumination wire through the hole in the illumination dovetail.
• Make renders in render.py
• Use renders in the instructions mount_illumination.md

Closes: #430 (closed)