[cxx]: GPIO CXX wrappers, experiemental CI rule

* Wrapper class for simple GPIO interaction
  like read/write without ISRs.
* Added rule to provoke builds after changes in
  the experimental C++ component.

examples/cxx/experimental/blink_cxx/main/main.cpp

@@ -0,0 +1,39 @@
+/* Blink C++ Example
+
+   This example code is in the Public Domain (or CC0 licensed, at your option.)
+
+   Unless required by applicable law or agreed to in writing, this
+   software is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR
+   CONDITIONS OF ANY KIND, either express or implied.
+*/
+
+#include <cstdlib>
+#include <thread>
+#include "esp_log.h"
+#include "gpio_cxx.hpp"
+
+using namespace idf;
+using namespace std;
+
+extern "C" void app_main(void)
+{
+    /* The functions of GPIO_Output throws exceptions in case of parameter errors or if there are underlying driver
+       errors. */
+    try {
+        /* This line may throw an exception if the pin number is invalid.
+         * Alternatively to 4, choose another output-capable pin. */
+        GPIO_Output gpio(GPIONum(4));
+
+        while (true) {
+            printf("LED ON\n");
+            gpio.set_high();
+            this_thread::sleep_for(std::chrono::seconds(1));
+            printf("LED OFF\n");
+            gpio.set_low();
+            this_thread::sleep_for(std::chrono::seconds(1));
+        }
+    } catch (GPIOException &e) {
+        printf("GPIO exception occurred: %s\n", esp_err_to_name(e.error));
+        printf("stopping.\n");
+    }
+}