scadr: renders multi-part OpenSCAD files

This solves a few very annoying problems:

Given an OpenSCAD file that produces multiple parts, how do I get an .stl file for each of them?

and

How do I easily make an OpenSCAD file that renders in low resolution in preview, but high resolution in output?

This solution doesn't require any awkward makefiles or other scripts and can just use a module naming convention. I like it.