4-12: Add example 4_12_ESP_NOW to demonstrate ESP-NOW startup & shutdown

Example_Sketches/4_12_ESP_NOW/4_12_ESP_NOW.ino

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+/**********************************************************************
+  4_12_ESP_NOW.ino
+
+  Example sketch to demonstrate ESP_NOW startup
+**********************************************************************/
+
+//****************************************
+// Includes
+//****************************************
+
+#include <Arduino.h>    // Built-in
+#include <ESPmDNS.h>    // Built-in
+#include <MacAddress.h> // Built-in
+#include <Network.h>    // Built-in
+#include <WiFi.h>       // Built-in
+
+#include "esp_now.h"        // IDF built-in
+#include "esp_mac.h"        // IDF built-in
+#include <esp_wifi.h>       // IDF built-in
+#include "esp_wifi_types.h" // IDF built-in
+
+#include <secrets.h>    // Host name, SSIDs and passwords
+
+bool RTK_CONFIG_MBEDTLS_EXTERNAL_MEM_ALLOC = false;
+
+#define systemPrintf    Serial.printf
+#define systemPrintln   Serial.println
+
+//****************************************
+// WiFi class
+//****************************************
+
+//*********************************************************************
+// Entry point for the application
+void setup()
+{
+    // Initialize the USB serial port
+    Serial.begin(115200);
+    systemPrintln();
+    systemPrintf(__FILE__ "\r\n");
+}
+
+//*********************************************************************
+// Idle loop for core 1 of the application
+void loop()
+{
+    espNowTest();
+}