Add HardwareSerial::write(const char *)

fixes: https://github.com/espressif/arduino-esp32/issues/55

cores/esp32/HardwareSerial.h

@@ -46,6 +46,10 @@ public:
     size_t write(uint8_t);
     size_t write(const uint8_t *buffer, size_t size);
 
+    inline size_t write(const char * s)
+    {
+        return write((uint8_t*) s, strlen(s));
+    }
     inline size_t write(unsigned long n)
     {
         return write((uint8_t) n);