add Chapter13

Chapter13/uart_c_hal_wrapper/app/src/main.cpp

@@ -0,0 +1,26 @@
+#include <cstdint>
+#include <cstdio>
+
+#include <stm32f072xb.h>
+
+#include <hal.hpp>
+#include <stm32f0xx_hal_uart.hpp>
+#include <uart_stm32.hpp>
+
+#include <retarget.hpp>
+
+int main()
+{
+    hal::init();
+
+    hal::uart_stm32<hal::stm32::uart> uart(USART2);
+    uart.init();
+
+    retarget::set_stdio_uart(&uart);
+    
+    printf("Hello world\r\n");
+    
+    while(true)
+    {
+    }
+}