[iagno] Add help overlay.

[Arnaud B. <arnaudb src gnome org>]

commit 9bcd68b3cef8394b3632baca1cea74dd01b810c7
Author: Arnaud Bonatti <arnaud bonatti gmail com>
Date:   Mon Jul 29 13:22:34 2019 +0200

    Add help overlay.

 data/iagno.gresource.xml |   3 ++
 data/ui/help-overlay.ui  | 138 +++++++++++++++++++++++++++++++++++++++++++++++
 src/iagno.vala           |   1 +
 3 files changed, 142 insertions(+)
---
diff --git a/data/iagno.gresource.xml b/data/iagno.gresource.xml
index 7d329b5..4c4b563 100644
--- a/data/iagno.gresource.xml
+++ b/data/iagno.gresource.xml
@@ -14,4 +14,7 @@
     <file preprocess="xml-stripblanks" compressed="true" alias="overlayed-list.ui"          
> ui/overlayed-list.ui</file>
     <file preprocess="xml-stripblanks" compressed="true" alias="registry-placeholder.ui"    
> ui/registry-placeholder.ui</file>
   </gresource>
+  <gresource prefix="/org/gnome/Reversi/gtk">
+    <file preprocess="xml-stripblanks" alias="help-overlay.ui">ui/help-overlay.ui</file>
+  </gresource>
 </gresources>
diff --git a/data/ui/help-overlay.ui b/data/ui/help-overlay.ui
new file mode 100644
index 0000000..206ff7c
--- /dev/null
+++ b/data/ui/help-overlay.ui
@@ -0,0 +1,138 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<!--
+  This file is part of GNOME Reversi (also known as Iagno).
+
+  Copyright 2019 Arnaud Bonatti
+
+  GNOME Reversi is free software: you can redistribute it and/or modify
+  it under the terms of the GNU General Public License as published by
+  the Free Software Foundation, either version 3 of the License, or
+  (at your option) any later version.
+
+  GNOME Reversi is distributed in the hope that it will be useful,
+  but WITHOUT ANY WARRANTY; without even the implied warranty of
+  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+  GNU General Public License for more details.
+
+  You should have received a copy of the GNU General Public License
+  along with GNOME Reversi.  If not, see <https://www.gnu.org/licenses/>.
+-->
+<interface domain="iagno">
+  <requires lib="gtk+" version="3.12"/>
+  <object class="GtkShortcutsWindow" id="help_overlay">
+    <child>
+      <object class="GtkShortcutsSection">
+        <property name="visible">True</property>
+        <property name="max-height">8</property>
+        <child>
+          <object class="GtkShortcutsGroup">
+            <property name="visible">True</property>
+            <property name="title" translatable="yes" context="shortcut window">During game 
selection</property>
+            <child>
+              <object class="GtkShortcutsShortcut">
+                <property name="visible">True</property>
+                <property name="title" translatable="yes" context="shortcut window">Start new game</property>
+                <property name="accelerator">&lt;Primary&gt;&lt;Shift&gt;n</property>
+              </object>
+            </child>
+            <child>
+              <object class="GtkShortcutsShortcut">
+                <property name="visible">True</property>
+                <property name="title" translatable="yes" context="shortcut window">Go back</property>
+                <property name="accelerator">Escape</property>
+              </object>
+            </child>
+          </object>
+        </child>
+        <child>
+          <object class="GtkShortcutsGroup">
+            <property name="visible">True</property>
+            <property name="title" translatable="yes" context="shortcut window">Play with keyboard</property>
+            <child>
+              <object class="GtkShortcutsShortcut">
+                <property name="visible">True</property>
+                <property name="title" translatable="yes" context="shortcut window">Select where to 
play</property>
+                <property name="accelerator">Left Right Up Down</property>
+              </object>
+            </child>
+            <child>
+              <object class="GtkShortcutsShortcut">
+                <property name="visible">True</property>
+                <property name="title" translatable="yes" context="shortcut window">Select the given 
row</property>
+                <property name="accelerator">1...8</property>
+              </object>
+            </child>
+            <child>
+              <object class="GtkShortcutsShortcut">
+                <property name="visible">True</property>
+                <property name="title" translatable="yes" context="shortcut window">Select the given 
column</property>
+                <property name="accelerator">a...h</property>
+              </object>
+            </child>
+            <child>
+              <object class="GtkShortcutsShortcut">
+                <property name="visible">True</property>
+                <property name="title" translatable="yes" context="shortcut window">Play on selected 
tile</property>
+                <property name="accelerator">Return space</property>
+              </object>
+            </child>
+          </object>
+        </child>
+        <child>
+          <object class="GtkShortcutsGroup">
+            <property name="visible">True</property>
+            <property name="title" translatable="yes" context="shortcut window">During a game</property>
+            <child>
+              <object class="GtkShortcutsShortcut">
+                <property name="visible">True</property>
+                <property name="title" translatable="yes" context="shortcut window">New game</property>
+                <property name="accelerator">&lt;Primary&gt;n</property>
+              </object>
+            </child>
+            <child>
+              <object class="GtkShortcutsShortcut">
+                <property name="visible">True</property>
+                <property name="title" translatable="yes" context="shortcut window">Undo last move</property>
+                <property name="accelerator">&lt;Primary&gt;z</property>
+              </object>
+            </child>
+          </object>
+        </child>
+        <child>
+          <object class="GtkShortcutsGroup">
+            <property name="visible">True</property>
+            <property name="title" translatable="yes" context="shortcut window">Generic</property>
+            <child>
+              <object class="GtkShortcutsShortcut">
+                <property name="visible">True</property>
+                <property name="title" translatable="yes" context="shortcut window">Keyboard 
shortcuts</property>
+                <property name="accelerator">&lt;Primary&gt;question &lt;Primary&gt;F1</property>
+              </object>
+            </child>
+            <child>
+              <object class="GtkShortcutsShortcut">
+                <property name="visible">True</property>
+                <property name="title" translatable="yes" context="shortcut window">Help</property>
+                <property name="accelerator">F1</property>
+              </object>
+            </child>
+            <child>
+              <object class="GtkShortcutsShortcut">
+                <property name="visible">True</property>
+                <property name="title" translatable="yes" context="shortcut window">About</property>
+                <property name="accelerator">&lt;Shift&gt;F1</property>
+              </object>
+            </child>
+            <child>
+              <object class="GtkShortcutsShortcut">
+                <property name="visible">True</property>
+                <property name="title" translatable="yes" context="shortcut window">Quit</property>
+                <property name="accelerator">&lt;Primary&gt;q</property>
+              </object>
+            </child>
+          </object>
+        </child>
+      </object>
+    </child>
+  </object>
+</interface>
diff --git a/src/iagno.vala b/src/iagno.vala
index 333875e..54dfd96 100644
--- a/src/iagno.vala
+++ b/src/iagno.vala
@@ -287,6 +287,7 @@ private class Iagno : Gtk.Application, BaseApplication
                                  start_now,
                                  GameWindowFlags.SHOW_START_BUTTON
                                  | GameWindowFlags.HAS_SOUND
+                                 | GameWindowFlags.SHORTCUTS
                                  | GameWindowFlags.SHOW_HELP
                                  | GameWindowFlags.SHOW_UNDO,
                                  (Box) new_game_screen,