Add visibility attributes to rcp_managed()

include/rcp.h

@@ -113,12 +113,14 @@ public:
         mutable std::atomic<int> ref_count{0}
 
 #define rcp_managed(classname) \
-    rcp<classname> get_rcp() \
-    { \
-        return rcp<classname>(this); \
-    } \
-    template <typename... Args> \
-    static rcp<classname> create(Args&&... args) \
-    { \
-        return (new classname(std::forward<Args>(args)...))->get_rcp(); \
-    }
+    public: \
+        rcp<classname> get_rcp() \
+        { \
+            return rcp<classname>(this); \
+        } \
+        template <typename... Args> \
+        static rcp<classname> create(Args&&... args) \
+        { \
+            return (new classname(std::forward<Args>(args)...))->get_rcp(); \
+        } \
+    private: