Fix HardwareSerial::flush()

Author: edogaldo

STM32F1/cores/maple/HardwareSerial.cpp

@@ -194,4 +194,5 @@ size_t HardwareSerial::write(unsigned char ch) {
 
 void HardwareSerial::flush(void) {
     usart_reset_rx(this->usart_device);
+    usart_reset_tx(this->usart_device);
 }

STM32F1/system/libmaple/include/libmaple/usart.h

@@ -396,7 +396,7 @@ typedef struct usart_dev {
                                       * Actual RX buffer used by rb.
                                       * This field will be removed in
                                       * a future release. */
-    uint8 tx_buf[USART_TX_BUF_SIZE]; /* Actual TX buffer used by wb */
+    uint8 tx_buf[USART_TX_BUF_SIZE]; /**< Actual TX buffer used by wb */
     rcc_clk_id clk_id;               /**< RCC clock information */
     nvic_irq_num irq_num;            /**< USART NVIC interrupt */
 } usart_dev;