Add hands unit for length (#634)

Author: tmilnthorp

Common/UnitDefinitions/Length.json

@@ -279,6 +279,21 @@
           "Abbreviations": [ "twip" ]
         }
       ]
+    },
+    {
+      "SingularName": "Hand",
+      "PluralName": "Hands",
+      "BaseUnits": {
+        "L": "Hand"
+      },
+      "FromUnitToBaseFunc": "x * 1.016e-1",
+      "FromBaseToUnitFunc": "x / 1.016e-1",
+      "Localization": [
+        {
+          "Culture": "en-US",
+          "Abbreviations": [ "h", "hh" ]
+        }
+      ]
     }
   ]
 }

UnitsNet.Tests/CustomCode/LengthTests.cs

@@ -53,7 +53,9 @@ public class LengthTests : LengthTestsBase
 
         protected override double NauticalMilesInOneMeter => 1.0/1852.0;
 
-        [Fact]
+        protected override double HandsInOneMeter => 9.8425196850393701;
+
+        [ Fact]
         public void AreaTimesLengthEqualsVolume()
         {
             Volume volume = Area.FromSquareMeters(10)*Length.FromMeters(3);