While gtk-doc doesn't care, this isn't really valid Markdown as the
GtkBuilder custom XML tags will be considered valid markup and embedded
as they are, breaking the HTML output.
We've recently a number of classes wholly. For these cases,
move the headers and sources to gtk/deprecated/ and adjust
Makefiles and includes accordingly.
Affected classes:
GtkAction
GtkActionGroup
GtkActivatable
GtkIconFactory
GtkImageMenuItem
GtkRadioAction
GtkRecentAction
GtkStock
GtkToggleAction
GtkUIManager