add Chapter04 bare example

Chapter04/bare/hal/inc/hal.hpp

@@ -0,0 +1,21 @@
+#pragma once
+
+#include <cstdint>
+
+#include <stm32f0xx_hal.h>
+
+namespace hal
+{
+inline void init()
+{
+    HAL_Init();
+}
+
+struct time
+{
+    inline static std::uint32_t get_ms()
+    {
+        return HAL_GetTick();
+    }
+};
+}; // namespace hal