HASensor improvements (#222)

* added support for setting None value in the HASensor

* added support for the expire_after property in the HASensor

* update readme and docs

* added expire_after property in the HABinarySensor

* increase default device types limit to 24 on non ATMega328/168 processors

* added support for the JSON attributes in the HASensor

examples/cover/cover.ino

@@ -15,6 +15,7 @@ HACover cover("myCover", HACover::PositionFeature);
 // PositionFeature is optional, however required to be in a "stopped" state other than open or closed.
 // If ommitted, a CommandStop will result in HA treating the cover as either Open or Closed immediately after the command.
 // See https://www.home-assistant.io/integrations/cover.mqtt/
+// Added in https://github.com/dawidchyrzynski/arduino-home-assistant/pull/111
 
 void onCoverCommand(HACover::CoverCommand cmd, HACover* sender) {
     if (cmd == HACover::CommandOpen) {

examples/sensor-analog/sensor-analog.ino

@@ -44,5 +44,8 @@ void loop() {
 
         analogSensor.setValue(voltage);
         lastUpdateAt = millis();
+
+        // you can reset the sensor as follows:
+        // analogSensor.setValue(nullptr);
     }
 }

examples/sensor-integer/sensor-integer.ino

@@ -37,5 +37,8 @@ void loop() {
         unsigned long uptimeValue = millis() / 1000;
         uptimeSensor.setValue(uptimeValue);
         lastUpdateAt = millis();
+
+        // you can reset the sensor as follows:
+        // analogSensor.setValue(nullptr);
     }
 }