Refactor `addTriangle()`.

Add:
	src/graphics/matrix.(c, h)
		-Redeclare `addTriangle()` to accept `Point_t` arguments. Seeing as the
		function is probably the most universally used method of point
		addition, its restructuring knocks out most of the work.
		-Add `COPY_POINT()`, for cases (like in `addSphere()`), where the same
		points occur time and time again in the same `Matrix_t`.

	src/(graphics/matrix, interpreter/interpreter).c
		-Rewrite all function calls to `addTriangle()`.

	test/testAddSphere.csv
		-Update the `addSphere` unit test file to reflect the new method of
		rendering spheres (with scanline fills).