Add per-declaration support for decl maps.

src/AST/Declaration.cs

@@ -334,6 +334,9 @@ namespace CppSharp.AST
 
         public List<Declaration> Redeclarations { get; } = new List<Declaration>();
 
+        // Custom declaration map for custom code generation.
+        public object DeclMap { get; set; }
+
         protected Declaration()
         {
             Access = AccessSpecifier.Public;
@@ -372,6 +375,7 @@ namespace CppSharp.AST
             LineNumberEnd = declaration.LineNumberEnd;
             IsImplicit = declaration.IsImplicit;
             AssociatedDeclaration = declaration.AssociatedDeclaration;
+            DeclMap = declaration.DeclMap;
         }
 
         public override string ToString()

src/Generator/Types/DeclMapDatabase.cs

@@ -60,6 +60,12 @@ namespace CppSharp.Types
 
         public bool FindDeclMap(Declaration decl, out DeclMap declMap)
         {
+            if (decl.DeclMap != null)
+            {
+                declMap = decl.DeclMap as DeclMap;
+                return true;
+            }
+
             // Looks up the decl in the cache map.
             if (declMaps.ContainsKey(decl))
             {