[struct_xml, struct_json, struct_yaml][feat]support shared_ptr

[qicosmos]

Why

support smart pointer in struct.

What is changing

Example

struct shared_object {
  std::shared_ptr<std::vector<std::shared_ptr<int>>> vec;
  std::string b;
  std::shared_ptr<int> c;
  std::vector<std::shared_ptr<int>> d;
};
REFLECTION(shared_object, vec, b, c, d);

void test_sp() {
  auto vec = std::make_shared<std::vector<std::shared_ptr<int>>>();
  vec->push_back(std::make_unique<int>(42));
  vec->push_back(std::make_unique<int>(21));
  shared_object contents{std::move(vec),
                         "test",
                         std::make_shared<int>(24),
                         {std::make_shared<int>(1), std::make_shared<int>(4)}};
  std::string str;
  iguana::to_xml(contents, str);

  shared_object cont;
  iguana::from_xml(cont, str);  // throw exception.
  std::cout << cont.b << "\n";
}