Extended Archimedean Spiral Module

While designing a pancake-primary mounting fixture for a Musical Tesla Coil, I needed to generate an Archimedean Spiral to simulate the location of the primary wire in the fixture. I found the [Archimedean Spiral Module](https://www.thingiverse.com/thing:1267784) here on Thingiverse and it was a great starting point. However, it only starts at an initial radius of 0 and only lets you specify the final radius, which led to wrong spacing and positioning for my application.

Instead, I needed to be able to give a starting radius and a spacing for the spirals, and add an arbitrary start angle to rotate it to the correct angle for the fixture. So I modified the module and created this Extended Archimedean Spiral Module.

This module contains the `archimedean_spiral_ex()` function with the following parameters:
`spirals` = how many spirals (positive=CCW, negative=CW), can include partial spirals
`thickness` = how thick you want the arms to be
`startradius` = beginning radius