Stevenson Screen - modular, screw version

A modular, customizable weather protector (Stevenson screen) for weather sensors. This remix replaces the snap-together mechanism with screws for a more robust construction, changes the shell design to maintain constant thickness, and adds two new layer types: upper (no hole, intended to mount the top of the sensor to) and fan (which accommodates a small DC fan to improve airflow). It also adds a cable hole to the bottom layer.

**Usage**: Open the .scad file and enter the bounding box of your