OpenSCAD model for Case for PinePhone

based on [beattie's earlier model](https://github.com/beattie/PinePhone-Case).

files:
- case.scad: top-level/entrypoint.
- defaults.scad: tunable settings which affect the detail of the model.
- dimensions.scad: measurements of the actual PinePhone, used to assemble the bits.
- phone.scad: model of the actual PinePhone itself; the case is made by constructing a shell from this model.
- bits.scad: models of all the cutouts/extrusions which exist on the phone. i.e. buttons, ports, camera.

## use
- compile the scad to stl:
```
make build/case.stl
```

- slice the stl file using slic3r:
```
make build/case.gcode
```

- then send `build/case.gcode` to your printer.