Added simple (albeit in many cases suboptiomal) c_sleep() method for coroutines.

source/mijin/async/coroutine_sleep.hpp

@@ -0,0 +1,27 @@
+
+
+#pragma once
+
+#if !defined(MIJIN_ASYNC_COROUTINE_SLEEP_HPP_INCLUDED)
+#define MIJIN_ASYNC_COROUTINE_SLEEP_HPP_INCLUDED 1
+
+#include <chrono>
+#include "./coroutine.hpp"
+
+namespace mijin
+{
+template<typename Rep, typename Period>
+Task<> c_sleep(std::chrono::duration<Rep, Period> duration)
+{
+    auto now = std::chrono::high_resolution_clock::now();
+    const auto end = now + duration;
+    while (now < end)
+    {
+        co_await c_suspend();
+        now = std::chrono::high_resolution_clock::now();
+    }
+    co_return;
+}
+} // namespace mijin
+
+#endif // !defined(MIJIN_ASYNC_COROUTINE_SLEEP_HPP_INCLUDED)