OpenAPS Pi+Hat 2x18650 Case

UPDATE: Assembled cases now available for purchase:
[I've opened an etsy shop to sell fully assembled versions of this case.](https://www.etsy.com/listing/767396083/openaps-rugged-pihat-case-two-18650?ref=shop_home_active_1)

I have also updated most files with final versions:

* 2x_top_final.stl
* 2x_bottom_final.stl
* 2x_negterm_final.stl
* 2x_posterm_final.stl
* 2x_door_final.stl
* genericpositive_final.stl

These updates are compatible with the other parts, but make the case significantly easier to build. The tops and bottom now have custom supports, so do not split these to objects. Support is not needed unless you choose to not use the custom supports. No supports versions are also included.

Captive M3 hex nuts have replaced heat set inserts for easier builds, simply insert the nut into the slot and use a short M3 screw to pull it up into the retaining area. Depending on printer tolerances, you may need a tiny spot of superglue or epoxy to retain the nu