Replace managed class with rcp_managed macro

include/rcp.h

@@ -123,16 +123,14 @@ public:
     }
 };
 
-template <typename T>
-class managed
-{
-public:
-    static_assert(std::is_base_of<root, T>::value,
-            "T must inherit from rcp::root to use rcp::managed<T>");
-
-    rcp<T> get_rcp()
-    {
-        root * r = (root *)this;
-        return rcp<T>(r->get_root_rcp());
+#define rcp_managed(classname) \
+    rcp<classname> get_rcp() \
+    { \
+        root * r = (root *)this; \
+        return rcp<classname>(r->get_root_rcp()); \
+    } \
+    template <typename... Args> \
+    static rcp<classname> create(Args&&... args) \
+    { \
+        return (new classname(std::forward<Args>(args)...))->get_rcp(); \
     }
-};