add sensor example

examples/sensor/sensor.ino

@@ -0,0 +1,49 @@
+#include <Ethernet.h>
+#include <ArduinoHA.h>
+
+byte mac[] = {0x00, 0x10, 0xFA, 0x6E, 0x38, 0x4A};
+unsigned long lastSentAt = millis();
+double lastValue = 0;
+
+EthernetClient client;
+HADevice device(mac, sizeof(mac));
+HAMqtt mqtt(client, device);
+
+/**
+ * Supported data types:
+ * - uint8_t
+ * - uint16_t (unsigned int)
+ * - uint32_t (unsigned long)
+ * - int8_t
+ * - int16_t (int)
+ * - int32_t (long)
+ * - double
+ * - float
+ */
+HASensor<double> temp("temp", 0, mqtt);
+
+void setup() {
+    // you don't need to verify return status
+    Ethernet.begin(mac);
+
+    // set device's details (optional)
+    device.setName("Arduino");
+    device.setSoftwareVersion("1.0.0");
+
+    // you can set custom units for the sensor (optional)
+    temp.setUnitOfMeasurement("°C");
+
+    // please change IP address to yours
+    mqtt.begin(IPAddress(192,168,0,17));
+}
+
+void loop() {
+    Ethernet.maintain();
+    mqtt.loop();
+
+    if ((millis() - lastSentAt) >= 5000) {
+        lastSentAt = millis();
+        lastValue = lastValue + 0.5;
+        temp.setValue(lastValue);
+    }
+}