Add decameters (#1036)

Author: tmilnthorp

Common/UnitDefinitions/Length.json

@@ -14,7 +14,7 @@
       },
       "FromUnitToBaseFunc": "{x}",
       "FromBaseToUnitFunc": "{x}",
-      "Prefixes": [ "Nano", "Micro", "Milli", "Centi", "Deci", "Hecto", "Kilo" ],
+      "Prefixes": [ "Nano", "Micro", "Milli", "Centi", "Deci", "Deca", "Hecto", "Kilo" ],
       "Localization": [
         {
           "Culture": "en-US",

UnitsNet.NanoFramework/GeneratedCode/Quantities/Length.g.cs

@@ -76,6 +76,8 @@ public class LengthTests : LengthTestsBase
 
         protected override double ChainsInOneMeter => 0.0497096953789867;
 
+        protected override double DecametersInOneMeter => 1e-1;
+
         [ Fact]
         public void AreaTimesLengthEqualsVolume()
         {