fix[cxx]: improve experimental cxx examples

* use std::this_thread::sleep_for instead of
  FreeRTOS sleep functions
* adjusted/added lincense headers in examples

examples/cxx/experimental/esp_event_async_cxx/main/esp_event_async_cxx_example.cpp

@@ -6,6 +6,7 @@
    software is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR
    CONDITIONS OF ANY KIND, either express or implied.
 */
+
 #include <iostream>
 #include "esp_event_cxx.hpp"
 #include "esp_event.h"

examples/cxx/experimental/esp_timer_cxx/main/esp_timer_example.cpp

@@ -1,20 +1,15 @@
-// Copyright 2020 Espressif Systems (Shanghai) PTE LTD
-//
-// Licensed under the Apache License, Version 2.0 (the "License");
-// you may not use this file except in compliance with the License.
-// You may obtain a copy of the License at
-//
-//         http://www.apache.org/licenses/LICENSE-2.0
-//
-// Unless required by applicable law or agreed to in writing, software
-// distributed under the License is distributed on an "AS IS" BASIS,
-// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
-// See the License for the specific language governing permissions and
-// limitations under the License.
+/* ESP Timer 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 <iostream>
-#include "freertos/FreeRTOS.h"
-#include "freertos/task.h"
+#include <thread>
+#include <chrono>
 
 #include "esp_timer_cxx.hpp"
 #include "esp_exception.hpp"
@@ -30,14 +25,13 @@ extern "C" void app_main(void)
         ESPTimer timer([]() { cout << "timeout" << endl; });
         timer.start(chrono::microseconds(200 * 1000));
 
-        vTaskDelay(550 / portTICK_PERIOD_MS);
+        this_thread::sleep_for(std::chrono::milliseconds(550));
 
         cout << "Setting up timer to trigger periodically every 200ms" << endl;
         ESPTimer timer2([]() { cout << "periodic timeout" << endl; });
         timer2.start_periodic(chrono::microseconds(200 * 1000));
 
-        vTaskDelay(1050 / portTICK_PERIOD_MS);
-
+        this_thread::sleep_for(std::chrono::milliseconds(1050));
     } catch (const ESPException &e) {
         cout << "Exception with error: " << e.error << endl;
     }

examples/cxx/experimental/sensor_mcp9808/main/sensor_mcp9808.cpp

@@ -1,3 +1,12 @@
+/* ESP MCP9808 Sensor/I2C 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 <iostream>
 #include "i2c_cxx.hpp"