Replacement Solidoodle extruder with quick release

This is a printable replacement for the fragile stock Solidoodle "jigsaw" extruder assembly. Heavily inspired by Lawsy's excellent Mk5 extruder design (but built from scratch in openSCAD), it incorporates some improvements I personally wanted to add.

Additions include a flip-up quick-release latch for tension arm and beefed-up hinge pivot points. Also added are an optional swinging mount for a small 25mm peek-assembly cooling fan, and a connector bracket to hold the type of coax power conne