Close virtual world
This method changes the virtual world from an opened to a closed state:
If the world was opened more than once, you must use an appropriate number of close calls before the virtual world closes.
If vrworld_object is a vector of vrworld objects, all associated virtual worlds close.
If the virtual world is already closed, close does nothing.
Opening and closing virtual worlds is a mechanism of memory management. When the system needs more memory and the virtual world is closed, you can discard its contents at any time.
Generally, you should close a virtual world when you no longer need it. This allows you to reuse the memory it occupied. The vrworld objects associated with this virtual world stay valid after it is closed, so the virtual world can be opened again without creating a new vrworld object.