Ignored protected members of value types. Used a constant for the instance identifier to improve performance.

Signed-off-by: Dimitar Dobrev <dpldobrev@yahoo.com>

src/Generator/Generators/CSharp/CSharpTextTemplate.cs

@@ -61,10 +61,7 @@ namespace CppSharp.Generators.CSharp
             return "Winapi";
         }
 
-        public static string InstanceIdentifier
-        {
-            get { return Generator.GeneratedIdentifier("Instance"); }
-        }
+        public const string InstanceIdentifier = "__Instance";
 
         public static string GetAccess(AccessSpecifier accessSpecifier)
         {

src/Generator/Passes/CheckIgnoredDecls.cs

@@ -14,6 +14,9 @@ namespace CppSharp.Passes
             case AccessSpecifier.Public:
                 return true;
             case AccessSpecifier.Protected:
+                var @class = decl.Namespace as Class;
+                if (@class != null && @class.IsValueType)
+                    return false;
                 return generateNonPublicDecls;
             case AccessSpecifier.Private:
                 var method = decl as Method;