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

src/app_layout.cpp

@@ -5,7 +5,6 @@
 #include "node_text.h"
 #include "node_progress_bar.h"
 #include "node_dialog_picker.h"
-#include "node_about.h"
 
 using namespace ui;
 
@@ -547,6 +546,8 @@ void App::init_menu_about()
             };
 
             popup->find<NodeButtonCustom>("about-doc")->on_click = [this](Node*) {
+                auto path = Asset::absolute("data/doc/test.pdf");
+                display_file(path);
                 popup->mouse_release();
                 popup->destroy();
             };
@@ -560,6 +561,7 @@ void App::init_menu_about()
                     text->set_text(label);
                 }
                 item->on_click = [this](Node*) {
+                    dialog_changelog();
                     popup->mouse_release();
                     popup->destroy();
                 };