Adding basic refactoring

[MarkJeronimus]

I'm not a high-duty OpenSCAD user, but one of the things that it's editor lacks and I was looking for in a replacement, is the ability to intelligently rename variables or other identifiers (taking into account shadowed variables inside code blocks)

Other things I find myself doing a lot is extracting code to module, in-lining variables, and surrounding code by translate()/difference()/etc.

[Antyos]

Hi Mark, as I mentioned in #40, I think this is something that will be resolved by (or at least requires) the language server introduced by #31. The people who have worked on it previously seem to have moved on, and I haven't had the time to look into myself, so I don't know when that will happen.