json/tree: add from_json that takes a path

json/tree.hpp

@@ -379,4 +379,16 @@ from_json (const json::tree::node &n, Args&&... args)
     );
 }
 
+
+//-----------------------------------------------------------------------------
+template <typename T, class ...Args>
+T
+from_json (const std::experimental::filesystem::path &src, Args &&...args)
+{
+    return from_json<T> (
+        *json::tree::parse (src),
+        std::forward<Args> (args)...
+    );
+}
+
 #endif