Method normalize

jni/venus/vec3.h:110–110

	T length2() const { return x*x + y*y + z*z; }
	T length() const { return std::sqrt(x*x + y*y + z*z); }
	void normalize() { *this /= length(); }

	/**
	 * give the vector v a spherical coordinate system(rho, theta, phi) view.