Work on averaging adjacent surface normals.

Add:
	src/graphics/matrix.(c, h)
		-Add code to `drawMatrix()` to find the average of the surface
		normals of all triangles adjacent to another given triangle.

	src/graphics/graphics.(c, h)
		-Add `intToRgb()`; redefined `flatShade()` with `Light_t *`,
		instead of `Point_t *`, parameters.