Add enhancements

   change deprecated TEMP_CELSIUS to UnitOfTemperature.CELSIUS
   change deprecated SPEED_METERS_PER_SECOND to
   change deprecated LENGTH_MILLIMITERS to
   change unit of rain to mm/h
   remove unused import of WIND_SPEED
   add unique_id
   derive class WeatherSensor from SensorEntity instead of Entity
   set _attr_native_unit_of_measurement instead of _unit_of_measurement
   update native_value instead of state
   add dew_point to regular expression for values which can become negative
   define SensorDeviceClass for all measurements where SensorDeviceClass is available
   change direct access to class attributes to access via property

README.md

@@ -90,6 +90,7 @@ sensor:
     name: WeatherStation
     host: 192.168.178.2
     port: 45000
+    unique_id: ELV-2504508-94 # vendor-productid-sensorid
     monitored_conditions:
       - inside_temperature
       - outside_temperature