Ring-style PTC adapter for Groovemount Extruders

Needed a PTC adapter/mount for a groovemount-style extruder for a printer I have been building; so I made one. It seemed generally useful, so uploading it separately here.

SCAD files are available at the associated printer's [github](https://github.com/lordofhyphens/hexydelta-solid) repository as ptc.scad.