allow release notes window to be opened from command line * main-window.h, main-window.cc (main_window::m_release_notes_windoow, main_window::m_release_notes_icon): Delete member variables and all uses. (main_window::display_release_notes): Delete. (main_window::show_release_notes_signal): New signal. (main_window::construct_news_menu): Use lambda function to emit show_release_notes_signal. * release-notes.h, release-notes.cc: New files. * libgui/src/module.mk: Update. * octave-qobject.h, octave-qobject.cc (base_qobject::base_qobject): Connect main_window show_release_notes_signal to base_qobject show_release_notes slot. If gui_app is true, connect main_window show_release_notes_signal to base_qobject show_release_notes slot. (base_qobject::start_gui): Also connect main_window show_release_notes_signal to base_qobject show_release_notes slot here. (base_qobject::m_release_notes): New member variable. (base_qobject::release_notes_widget, base_qobject::show_release_notes): New functions. * qt-interpreter-events.h, qt-interpreter-events.cc (qt_interpreter_events::show_release_notes): New function. (qt_interpreter_events::show_release_notes_signal): New signal. * event-manager.h, event-manager.cc (event_manager::show_release_notes): New function. (interpreter_events::show_release_notes): New virtual function. (F__event_manager_show_release_notes__): New function.

--- a/libgui/src/qt-interpreter-events.h	Fri Jun 25 17:27:17 2021 -0400
+++ b/libgui/src/qt-interpreter-events.h	Sat Jun 26 07:59:17 2021 -0400
@@ -128,6 +128,7 @@
     void show_workspace (void);
 
     void show_community_news (int serial);
+    void show_release_notes (void);
 
     bool edit_file (const std::string& file);
 
@@ -282,6 +283,7 @@
     void show_workspace_signal (void);
 
     void show_community_news_signal (int serial);
+    void show_release_notes_signal (void);
 
     // Note: this signal currently not used by the old terminal widget.
     void interpreter_output_signal (const QString& msg);