Push-fit adaptor, for Bondtech BMG extruder with 6mm PTFE feed

Cheerfully presenting *yet another* Bowden-tube adaptor ;D

Here's some distinguishing features:
* Compatible with Bondtech (BMG) Mini Geared Extruder, and friends
* Adapts any BMG extruder to accept 6mm PTFE bowden-tube, via an easy push-fit
* Interfaces nicely with PolyMaker PolyBox (& similar) dry-filament cabinets, via 6mm PTFE
* 3D-modelled, as a parameteric OpenSCAD model.

Have fun