Add missing symbols to the docs

docs/reference/gtk/gtk3-sections.txt

@@ -139,6 +139,7 @@ gtk_accel_label_set_accel_closure
 gtk_accel_label_get_accel_widget
 gtk_accel_label_set_accel_widget
 gtk_accel_label_get_accel_width
+gtk_accel_label_set_accel
 gtk_accel_label_refetch
 <SUBSECTION Standard>
 GTK_ACCEL_LABEL
@@ -263,6 +264,8 @@ gtk_action_group_get_sensitive
 gtk_action_group_set_sensitive
 gtk_action_group_get_visible
 gtk_action_group_set_visible
+gtk_action_group_get_accel_group
+gtk_action_group_set_accel_group
 gtk_action_group_get_action
 gtk_action_group_list_actions
 gtk_action_group_add_action
@@ -530,6 +533,7 @@ gtk_builder_add_from_resource
 gtk_builder_add_from_string
 gtk_builder_add_objects_from_file
 gtk_builder_add_objects_from_string
+gtk_builder_add_objects_from_resource
 gtk_builder_get_object
 gtk_builder_get_objects
 gtk_builder_connect_signals
@@ -583,6 +587,8 @@ gtk_button_set_image
 gtk_button_get_image
 gtk_button_set_image_position
 gtk_button_get_image_position
+gtk_button_set_always_show_image
+gtk_button_get_always_show_image
 gtk_button_get_event_window
 
 <SUBSECTION Standard>
@@ -1810,6 +1816,7 @@ gtk_image_new_from_stock
 gtk_image_new_from_animation
 gtk_image_new_from_icon_name
 gtk_image_new_from_gicon
+gtk_image_new_from_resource
 gtk_image_set_from_file
 gtk_image_set_from_icon_set
 gtk_image_set_from_pixbuf
@@ -1817,6 +1824,7 @@ gtk_image_set_from_stock
 gtk_image_set_from_animation
 gtk_image_set_from_icon_name
 gtk_image_set_from_gicon
+gtk_image_set_from_resource
 gtk_image_clear
 gtk_image_new
 gtk_image_set_pixel_size
@@ -5978,6 +5986,7 @@ gtk_gradient_add_color_stop
 gtk_gradient_ref
 gtk_gradient_unref
 gtk_gradient_resolve
+gtk_gradient_resolve_for_context
 gtk_gradient_to_string
 
 <SUBSECTION Standard>
@@ -7110,6 +7119,7 @@ gtk_application_add_window
 gtk_application_remove_window
 gtk_application_get_windows
 gtk_application_get_window_by_id
+gtk_application_get_active_window
 
 <SUBSECTION>
 GtkApplicationInhibitFlags