src: Add IBUS_CAP_OSK to IBusCapabilite

Some IMEs' behavior is different between the on-screen keyboard and
the direct physical keyboard and this flag is useful for the IMEs.

Also fix src/ibusaccelgroup.c for gtkdoc-mkhtml.
If the API comment of IBusCapabilite is updated, XML & HTML files
are rebuilt and gtk-doc-1.33.2 no longer accepts HTML tags in
the comments.

src/ibusaccelgroup.c

@@ -267,14 +267,14 @@ is_keycode (const gchar *string)
  *     modifier mask, %NULL
  *
  * Parses a string representing an accelerator. The format looks like
- * “<Control>a” or “<Shift><Alt>F1” or “<Release>z” (the last one is
- * for key release).
+ * “&lt;Control&gt;a” or “&lt;Shift&gt;&lt;Alt&gt;F1” or “&lt;Release%gt;z”
+ * (the last one is for key release).
  *
  * The parser is fairly liberal and allows lower or upper case, and also
- * abbreviations such as “<Ctl>” and “<Ctrl>”. Key names are parsed using
- * gdk_keyval_from_name(). For character keys the name is not the symbol,
- * but the lowercase name, e.g. one would use “<Ctrl>minus” instead of
- * “<Ctrl>-”.
+ * abbreviations such as “&lt;Ctl&gt;” and “&lt;Ctrl&gt;”. Key names are
+ * parsed using gdk_keyval_from_name(). For character keys the name is not the
+ * symbol, but the lowercase name, e.g. one would use “&lt;Ctrl&gt;minus”
+ * instead of “&lt;Ctrl&gt;-”.
  *
  * If the parse fails, @accelerator_key and @accelerator_mods will
  * be set to 0 (zero).
@@ -403,7 +403,7 @@ ibus_accelerator_parse (const gchar      *accelerator,
  *
  * Converts an accelerator keyval and modifier mask into a string
  * parseable by gtk_accelerator_parse(). For example, if you pass in
- * #IBUS_KEY_q and #IBUS_CONTROL_MASK, this function returns “<Control>q”.
+ * #IBUS_KEY_q and #IBUS_CONTROL_MASK, this function returns “&lt;Control&gt;q”.
  *
  * If you need to display accelerators in the user interface,
  * see gtk_accelerator_get_label().

src/ibustypes.h

@@ -108,6 +108,7 @@ typedef enum
  * @IBUS_CAP_PROPERTY: UI is capable to have property.
  * @IBUS_CAP_SURROUNDING_TEXT: Client can provide surround text,
  *  or IME can handle surround text.
+ * @IBUS_CAP_OSK: UI is owned by on-screen keyboard.
  *
  * Capability flags of UI.
  */
@@ -118,6 +119,7 @@ typedef enum {
     IBUS_CAP_FOCUS              = 1 << 3,
     IBUS_CAP_PROPERTY           = 1 << 4,
     IBUS_CAP_SURROUNDING_TEXT   = 1 << 5,
+    IBUS_CAP_OSK                = 1 << 6,
 } IBusCapabilite;
 
 /**