Add temperature hysteresis

Do not refresh display if value not changed

bme280.ino

@@ -1,12 +1,23 @@
 #include "Seeed_BME280.h"
 
 BME280 sensor;
+float highTemp = 0.0, lowTemp = 0.0;
+const float blindZone = 0.03;
 
 void initBME280() {
   sensor.init();
 }
 
 void readTemperature() {
-  // TODO: add hysteresis
-  temperature = sensor.getTemperature();
+  float newTemperature = sensor.getTemperature();
+
+  if (newTemperature > highTemp) {
+    temperature = newTemperature;
+    highTemp = newTemperature;
+    lowTemp = highTemp - blindZone;
+  } else if (newTemperature < lowTemp) {
+    temperature = newTemperature;
+    lowTemp = newTemperature;
+    highTemp = lowTemp + blindZone;
+  };
 }