message: Return triangle_list by const reference
  It doesn't make too much sense to return by value here. If this was called in an inner loop, copying the triangle list repeatedly was actually quite an expensive operation.
diff: @@ -110,7 +110,7 @@ public:
  *
  * @return The list of triangles to build a mesh.
  */
  - std::vector<std::array<int, 3>> get_triangle_list() const
  + const std::vector<std::array<int, 3>>& get_triangle_list() const
  {
  return triangle_list;
  };
  