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>

main/config_DS1820.h

@@ -36,9 +36,9 @@ extern void pubOneWire_HADiscovery();
 #define DS1820_ALWAYS       true // if false only published current temperature if has changed from previous reading
 #define DS1820_INTERVAL_SEC 60 // time between DS1820 readings (seconds)
 #define DS1820_RESOLUTION   10 // conversion times: 9 bit (93.75 ms), 10 bit (187.5 ms), 11 bit (375 ms), 12 bit (750 ms)
-#ifndef DS1820_FAHRENHEIT
-#  define DS1820_FAHRENHEIT false // defaults to Celcius
-#endif
+#ifndef DS1820_FAHRENHEIT // remove for 0.9.6 release
+#  define DS1820_FAHRENHEIT false // defaults to Celcius // remove for 0.9.6 release
+#endif // remove for 0.9.6 release
 #define DS1820_DETAILS   true // publish extented info for each sensor (resolution, address, type)
 #define DS1820_CONV_TIME 2000 // trigger conversion before requesting temperature readings (ms)
 /*-------------------PIN DEFINITIONS----------------------*/