Add Btu/ft²·hr·°F to HeatTransferCoefficient (#670)

Author: tmilnthorp

Common/UnitDefinitions/HeatTransferCoefficient.json

@@ -31,6 +31,18 @@
           "Abbreviations": [ "W/m²·°C" ]
         }
       ]
+    },
+    {
+      "SingularName": "BtuPerSquareFootDegreeFahrenheit",
+      "PluralName": "BtusPerSquareFootDegreeFahrenheit",
+      "FromUnitToBaseFunc": "x * 5.6782633411134878",
+      "FromBaseToUnitFunc": "x / 5.6782633411134878",
+      "Localization": [
+        {
+          "Culture": "en-US",
+          "Abbreviations": [ "Btu/ft²·hr·°F" ]
+        }
+      ]
     }
   ]
 }

UnitsNet.Tests/CustomCode/HeatTransferCoefficientTests.cs

@@ -29,5 +29,6 @@ public class HeatTransferCoefficientTests : HeatTransferCoefficientTestsBase
     {
         protected override double WattsPerSquareMeterCelsiusInOneWattPerSquareMeterKelvin => 1;
         protected override double WattsPerSquareMeterKelvinInOneWattPerSquareMeterKelvin => 1;
+        protected override double BtusPerSquareFootDegreeFahrenheitInOneWattPerSquareMeterKelvin => 1.7611018368230584e-1;
     }
 }