Added converter Kelvin -> Celcius

src/main/java/no/nibio/vips/util/WeatherUtil.java

@@ -1554,6 +1554,16 @@ public class WeatherUtil {
         return (celciusTemp * 1.8) + 32;
     }
     
+    /**
+     * 
+     * @param kelvinTemp
+     * @return 
+     */
+    public double getCelciusFromKelvin(Double kelvinTemp)
+    {
+        return kelvinTemp - 273.15;
+    }
+    
     /**
      * Convert from inches to mm
      * @param inches