Make certain DigitalOut methods virtual

drivers/DigitalOut.h

@@ -70,12 +70,17 @@ class DigitalOut {
         gpio_init_out_ex(&gpio, pin, value);
     }
 
+    virtual ~DigitalOut()
+    {
+        gpio_free(&gpio);
+    }
+
     /** Set the output, specified as 0 or 1 (int)
      *
      *  @param value An integer specifying the pin output value,
      *      0 for logical 0, 1 (or any other non-zero value) for logical 1
      */
-    void write(int value)
+    virtual void write(int value)
     {
         // Thread safe / atomic HAL call
         gpio_write(&gpio, value);
@@ -87,7 +92,7 @@ class DigitalOut {
      *    an integer representing the output setting of the pin,
      *    0 for logical 0, 1 for logical 1
      */
-    int read()
+    virtual int read()
     {
         // Thread safe / atomic HAL call
         return gpio_read(&gpio);
@@ -99,7 +104,7 @@ class DigitalOut {
      *    Non zero value if pin is connected to uc GPIO
      *    0 if gpio object was initialized with NC
      */
-    int is_connected()
+    virtual int is_connected()
     {
         // Thread safe / atomic HAL call
         return gpio_is_connected(&gpio);