Adding protected parameterless constructor so SmartEnums are supported by EF (#16)

Author: mikaelweave

src/SmartEnum.UnitTests/TestEnum.cs

@@ -11,5 +11,10 @@ public class TestEnum : SmartEnum<TestEnum, int>
         protected TestEnum(string name, int value) : base(name, value)
         {
         }
+
+        private TestEnum() : base()
+        {
+            // required for EF
+        }
     }
 }

src/SmartEnum/SmartEnum.cs

@@ -39,6 +39,11 @@ protected SmartEnum(string name, TValue value)
             Value = value;
         }
 
+        protected SmartEnum()
+        {
+            // Required for EF
+        }
+
         public static TEnum FromName(string name)
         {
             Guard.Against.NullOrEmpty(name, nameof(name));