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 sensor (or thing) you want to put inside the weather protector. Tweak any other paremeters you want (they should be self-explanatory). Generate a top, upper (optional), middle, fan (optional) and bottom shell .stl, and print whatever you require. You can use the mount from [the original Thing](https://www.thingiverse.com/thing:2893269) or tweak the parameters to use your own mount.

.stl files included for reference.