Standardize MQTTDiscovery Temp Keys [deprecate tem key] (#703)

* Detect when sensor isn't available or read fails

* Add temperature conversion macros

* Add 'tempc' & 'tempf' keys to published values

* Unique Values for HA Discovery

* Remove degree symbol from temp sensors

Co-authored-by: Jonathan Michael Wells <jonathan-wells@oist.jp>

docs/use/sensors.md

@@ -5,11 +5,14 @@ Subscribe to all the messages with mosquitto or open your MQTT client software:
 
 ### ADC
 The value is between 0 and 1024 and is tranmitted via Mqtt when it changes.
-`home/OpenMQTTGateway/DHTtoMQTT {"value":543}`
+`home/OpenMQTTGateway/ADCtoMQTT {"value":543}`
 
 ### DHT
 You will receive every TimeBetweenReadingDHT (set into config_DHT.h) the DHT measurement (30s per default).
 
+`home/OpenMQTTGateway/DHTtoMQTT {"tempc":21,"tempf":69.8,"hum":51}`
+
+Legacy (removed after release 0.9.5)
 `home/OpenMQTTGateway/DHTtoMQTT {"temp":21,"hum":51}`
 
 If you want to don't resend value when it is the same you can set dht_always = false in config_DHT.h
@@ -32,6 +35,9 @@ If you don't want to resend values that haven't changed you can set AHTx0_always
 You will receive the DS18x20 sensor readings every DS1820_INTERVAL_SEC (set into config_DS1820.h) (60s by default).
 Each sensor will be published under the following topic using each sensors' address.
 
+`home/OpenMQTTGateway/CLIMAtoMQTT/ds1820/0x0000000000000000 {"tempc":27.8, "tempf":82.04, "type":"DS18B20","res":"12bit\n","addr":"0x28616411907650bc"}`
+
+Legacy (removed after release 0.9.5)
 `home/OpenMQTTGateway/CLIMAtoMQTT/ds1820/0x0000000000000000 {"temp":27.8,"unit":"C","type":"DS18B20","res":"12bit\n","addr":"0x28616411907650bc"}`
 
 The units for temperature readings are sent in Celcius by default can be changed to ferenheight by setting DS1820_FAHRENHEIT = true in in config_DS1820.h