OpenScad Virtual Machine - v0.2

Moving right along, adding some more convenience...

This thing builds on the last version of the OpenScad Virtual machine by adding a few convenience functions:

CUBE(size, center);
CYLINDER(r1, r2, h, center);
SPHERE(r);

And a couple for the CSG operations as well:

UNION(parts);
DIFFERENCE(part1, part2);

I also changed the 'CSG' module name to 'EXEC' which seems more appropriate.

So, now you can do this:

EXEC(UNION([CUBE([10,10,10]), CYLINDER(r1=6, r2=5, h=12)]);

That