Markup fixes.
* gdk-pixbuf/tmpl/creating.sgml,
gdk-pixbuf/tmpl/gdk-pixbuf-xlib-from-drawables.sgml,
gdk-pixbuf/tmpl/gdk-pixbuf-xlib-init.sgml,
gdk-pixbuf/tmpl/gdk-pixbuf-xlib-rendering.sgml,
gdk-pixbuf/tmpl/refcounting.sgml: Markup fixes.
* gtk/building.sgml, gtk/resources.sgml: Markup fixes.
* gtk/gtk.types: Remove gtk_text_layout_get_type(). (???)
* gdk/tmpl/general.sgml: Use <envar>, not <envvar>.
* gdk-pixbuf-io.c, gdk-pixbuf-animation.c, gdk-pixbuf-data.c,
gdk-pixbuf-loader.c, gdk-pixbuf-scale.c, gdk-pixbuf-util.c,
gdk-pixdata.c: Markup fixes.