message: Add function area(sphere)
diff: @@ -25,6 +25,13 @@ inline basic_sphere<T, P>::basic_sphere(vector<3, T> const& c, T r)
  // Geometric functions
  //
  +template <typename T, typename P>
  +MATH_FUNC
  +inline T area(basic_sphere<T, P> const& s)
  +{
  + return T(4.0) * constants::pi<T>() * s.radius * s.radius;
  +}
  +
  template <typename T, typename P>
  MATH_FUNC
  inline basic_aabb<T> get_bounds(basic_sphere<T, P> const& s)
  