docs: replace all figures with headings and images

gdk/gdkpango.c

@@ -119,10 +119,9 @@
  * g_object_unref (context);
  * ]|
  *
- * <figure>
- *   <title>Output of <xref linkend="rotated-example"/></title>
- *   <graphic fileref="rotated-text.png" format="PNG"/>
- * </figure>
+ * ## Output of <xref linkend="rotated-example"/>
+ *
+ * ![](rotated-text.png)
  */
 
 /* Get a clip region to draw only part of a layout. index_ranges

gtk/gtkapplication.c

@@ -81,17 +81,17 @@
  * GTK+ displays these menus as expected, depending on the platform
  * the application is running on.
  *
- * <figure label="Menu integration in OS X">
- * <graphic fileref="bloatpad-osx.png" format="PNG"/>
- * </figure>
+ * ## Menu integration in OS X
  *
- * <figure label="Menu integration in GNOME">
- * <graphic fileref="bloatpad-gnome.png" format="PNG"/>
- * </figure>
+ * ![](bloatpad-osx.png)
  *
- * <figure label="Menu integration in Xfce">
- * <graphic fileref="bloatpad-xfce.png" format="PNG"/>
- * </figure>
+ * ## Menu integration in GNOME
+ *
+ * ![](bloatpad-gnome.png)
+ *
+ * ## Menu integration in Xfce
+ *
+ * ![](bloatpad-xfce.png)
  *
  * ## A simple application ## {#gtkapplication}
  *

gtk/gtkcssprovider.c

@@ -595,21 +595,26 @@
  * animation will be repated until the state changes again.
  * The option after the duration determines the transition function from a
  * small set of predefined functions.
- * <figure><title>Linear transition</title>
- * <graphic fileref="linear.png" format="PNG"/>
- * </figure>
- * <figure><title>Ease transition</title>
- * <graphic fileref="ease.png" format="PNG"/>
- * </figure>
- * <figure><title>Ease-in-out transition</title>
- * <graphic fileref="ease-in-out.png" format="PNG"/>
- * </figure>
- * <figure><title>Ease-in transition</title>
- * <graphic fileref="ease-in.png" format="PNG"/>
- * </figure>
- * <figure><title>Ease-out transition</title>
- * <graphic fileref="ease-out.png" format="PNG"/>
- * </figure>
+ *
+ * ## Linear transition
+ *
+ * ![](linear.png)
+ *
+ * ## Ease transition
+ *
+ * ![](ease.png)
+ *
+ * ## Ease-in-out transition
+ *
+ * ![](ease-in-out.png)
+ *
+ * ## Ease-in transition
+ *
+ * ![](ease-in.png)
+ *
+ * ## Ease-out transition
+ *
+ * ![](ease-out.png)
  *
  * ## Supported properties
  *