Add TeraWh (#614)

* Add TeraWh

* And the unit test

Author: mivano

Common/UnitDefinitions/Energy.json

@@ -88,7 +88,7 @@
       "PluralName": "WattHours",
       "FromUnitToBaseFunc": "x*3600d",
       "FromBaseToUnitFunc": "x/3600d",
-      "Prefixes": [ "Kilo", "Mega", "Giga" ],
+      "Prefixes": [ "Kilo", "Mega", "Giga", "Tera" ],
       "Localization": [
         {
           "Culture": "en-US",

UnitsNet.Tests/CustomCode/EnergyTests.cs

@@ -49,6 +49,8 @@ public class EnergyTests : EnergyTestsBase
 
         protected override double ErgsInOneJoule => 10000000;
 
+        protected override double TerawattHoursInOneJoule => 2.77777778e-16;
+
         protected override double ThermsEcInOneJoule => 9.4781712031331720001278504447561e-9;
 
         protected override double FootPoundsInOneJoule => 0.737562149;