docs: fix gtk-doc warnings

Also add a couple of missing methods to the sections file
Properly annotate gdk_pixbuf_new_from_xpm_data

https://bugzilla.gnome.org/show_bug.cgi?id=668956

Signed-off-by: Martin Pitt <martinpitt@gnome.org>
Call size_func in io-gif so that pixbuf is aware of it.
Try to use animation size in the loader for animations.

Pixbuf size can be innacurate for some animations with frames of
different sizes.

Fixes: NB#613595
Pixbuf shall have at least 1 pixel when scaling
Changed doc of GdkPixbufAnimation about size management.

Animation frames can be a different size managing this should be done
through GdkPixbufAnimation.
Removed entities from the code markup as they are not being expanded
Updated Polish translation
Updated Spanish translation
Add missing allow-none anotations in animation API

https://bugzilla.gnome.org/show_bug.cgi?id=677477
Too much rounding when scaling the pixbufs.

The former code was causing that some frames where 1 pixel bigger than
the animation.
Updated Galician translations
Updated Serbian translation
Updated Slovenian translation
[l10n] Updated German translation
Improve man pages

Copy various tweaks that I've done to man pages in other
modules, to improve consistency.
2.26.2
Post-release bump
Updated Traditional Chinese translation(Hong Kong and Taiwan)
Assamese translation updated