Add 3d-shape commands to interpreter.

Add:
	src/interpreter/interpreter.c
		-add commands to add a rectangular prism, sphere, and torus to the
		current points matrix.
		-add command to clear the current points matrix.

	doc/interpreter.txt
		-add documentation for new interpreter commands.

	scripts/3d.gsc
		-add script to test functionality of 3D shape (rectangular prism,
		sphere, and torus)functions.