Add support for (rotate [[x y z]]).
This form corresponds with SCAD's rotate([x,y,z]).
Import STL files.
This can be done either by converting an STL file to a polyhedron,
which is a slow and memory hungry exercise for OpenSCAD, or by
passing the import directly through to OpenSCAD as an import(x);
directive.
Tweak version to x-AT to avoid confusion with fork.