easy timer

1. 功能

• priority_queue实现简单定时器
• 支持 std::function 添加，根据id删除
• 支持 时间点、循环、指定次数等，可嵌套组合使用

1. 使用示例：

   easy::Timer timer;
   bar b;
   std::vector<int> taskids;
   auto curr = system_clock::now();
   std::cout << "> timer " << ": " << (duration<double>(curr - now)).count() << "s => Start!" << std::endl;
   taskids.push_back(timer.add(foo, curr + seconds(2)));
   taskids.push_back(timer.add(std::bind(&bar::hello, b), curr + seconds(3), seconds(3), 3));
   taskids.push_back(timer.add(
   [ = ]() { std::cout << (duration<double>(system_clock::now() - now)).count() << "s => func lambda" << std::endl; },
   curr + seconds(4), seconds(2)));
   std::sleep_for(seconds(10));
   for (auto id : taskids)
   {
      std::cout << "> timer " << ": del " << id << std::endl;
      timer.del(id);
   }
   timer.stop();
   curr = system_clock::now();
   std::cout << "> timer " << ": " << (duration<double>(curr - now)).count() << "s => Stop!" << std::endl;

2. timer嵌套 每天一个定时器做当天任务：

   easy::Timer g_timer;
   g_timer.add([ = ]()
   {
      easy::Timer timer;
      bar b;
      std::vector<int> taskids;
      auto curr = system_clock::now();
      std::cout << "> timer " << ": " << (duration<double>(curr - now)).count() << "s => Start!" << std::endl;
      taskids.push_back(timer.add(foo, curr + seconds(2)));
      taskids.push_back(timer.add(std::bind(&bar::hello, b), curr + seconds(3), seconds(3), 3));
      taskids.push_back(timer.add(
      [ = ]() { std::cout << (duration<double>(system_clock::now() - now)).count() << "s => func lambda" << std::endl; },
      curr + seconds(4), seconds(2)));
      std::sleep_for(seconds(10));
      for (auto id : taskids)
      {
          std::cout << "> timer " << ": del " << id << std::endl;
          timer.del(id);
      }
      timer.stop();
      curr = system_clock::now();
      std::cout << "> timer " << ": " << (duration<double>(curr - now)).count() << "s => Stop!" << std::endl;
   },
   system_clock::now() + seconds(4), seconds(15));
   std::sleep_for(seconds(60));