add changelog dialog and display_file api (implemented in osx and ios)

src/app_events.cpp

@@ -63,6 +63,26 @@ void App::pick_image(std::function<void(std::string path)> callback)
 #endif
 }
 
+void App::display_file(std::string path)
+{
+#ifdef __IOS__
+    [ios_view display_file:path];
+#elif __OSX__
+    [[NSWorkspace sharedWorkspace] openFile:[NSString stringWithUTF8String:path.c_str()]];
+//    dispatch_async(dispatch_get_main_queue(), ^{
+//        std::string path = [osx_view pick_file];
+//        if (!path.empty())
+//            callback(path);
+//    });
+#elif __ANDROID__
+    //displayKeyboard(and_app, false);
+#elif _WIN32
+//    std::string path = win32_open_file();
+//    if (!path.empty())
+//        callback(path);
+#endif
+}
+
 bool App::mouse_down(int button, float x, float y, float pressure, kEventSource source)
 {
     redraw = true;