Cross-reference HdyDeck in documentation comments

Mention it in @See_also section of HdySwipeable, HdySwipeGroup and
HdySwipeTracker.
Signed-off-by: Alexander Mikhaylenko <alexm@gnome.org>

src/hdy-swipe-group.c

@@ -20,7 +20,7 @@
  * SECTION:hdy-swipe-group
  * @short_description: An object for syncing swipeable widgets.
  * @title: HdySwipeGroup
- * @See_also: #HdyCarousel, #HdyLeaflet, #HdySwipeable
+ * @See_also: #HdyCarousel, #HdyDeck, #HdyLeaflet, #HdySwipeable
  *
  * The #HdySwipeGroup object can be used to sync multiple swipeable widgets
  * that implement the #HdySwipeable interface, such as #HdyCarousel, so that

src/hdy-swipe-tracker.c

@@ -26,7 +26,7 @@
  * PRIVATE:hdy-swipe-tracker
  * @short_description: Swipe tracker used in #HdyCarousel and #HdyLeaflet
  * @title: HdySwipeTracker
- * @See_also: #HdyCarousel, #HdyLeaflet, #HdySwipeable
+ * @See_also: #HdyCarousel, #HdyDeck, #HdyLeaflet, #HdySwipeable
  * @stability: Private
  *
  * The HdySwipeTracker object can be used for implementing widgets with swipe

src/hdy-swipeable.c

@@ -10,14 +10,14 @@
  * SECTION:hdy-swipeable
  * @short_description: An interface for swipeable widgets.
  * @title: HdySwipeable
- * @See_also: #HdyCarousel, #HdyLeaflet, #HdySwipeGroup
+ * @See_also: #HdyCarousel, #HdyDeck, #HdyLeaflet, #HdySwipeGroup
  *
  * The #HdySwipeable interface is implemented by all swipeable widgets. They
  * can be synced using #HdySwipeGroup.
  *
  * #HdySwipeable is only meant to be used by libhandy widgets and is currently
- * implemented by #HdyCarousel and #HdyLeaflet. It should not be implemented
- * by applications.
+ * implemented by #HdyCarousel, #HdyDeck and #HdyLeaflet. It should not be
+ * implemented by applications.
  *
  * Since: 0.0.12
  */