[esp] Add ESP examples.

esp/cpp/01_led-button/01_led-button.ino

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+// set pin numbers
+const int buttonPin = 4;  // the number of the pushbutton pin
+const int ledPin =  5;    // the number of the LED pin
+
+// variable for storing the pushbutton status
+int buttonState = 0;
+
+bool light_on = false;
+bool handled = false;
+
+void setup() {
+  Serial.begin(115200);
+  // initialize the pushbutton pin as an input
+  pinMode(buttonPin, INPUT);
+  // initialize the LED pin as an output
+  pinMode(ledPin, OUTPUT);
+}
+
+void loop() {
+  // read the state of the pushbutton value
+  buttonState = digitalRead(buttonPin);
+  // check if the pushbutton is pressed.
+  if (buttonState == HIGH) {
+    if (!handled) {
+      Serial.println("Handling button pressed.");
+      light_on = !light_on;
+      handled = true;
+      digitalWrite(ledPin, light_on ? HIGH : LOW);
+    }
+    // turn LED on
+  } else {
+    if (handled) {
+      Serial.println("Reset button handled state.");
+      handled = false;
+
+    }
+  }
+}

esp/cpp/01_led-button/README.md

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+# 01_led-button
+
+![schematic](./schematic.png)
+
+Simple LED controlled by an on-board button.