Widget style properties can now have different values depending on the
current state.

Background will be actually rotated in tabs, so the "bottom" side coincides
with the junction point, this makes gradients work as expected in rotated tabs.

In addition to -gtk-gradient(...), allow url(path), and create
a pattern from the image. Still to do: allow stretch/repeat options.

Turns out "trough" as a detail string is used in a variety
of widgets, not all of which are scrollbars.

Move GtkGradient to their own files, also move GtkBorder out of
gtkstyle.h, so that header can be all deprecated.

This will probably need some finetuning.

Add some hints about dealing with colors.

We might end removing it altogether since it is a bit silly to have
Since: 3.0
Deprecated: 3.0

Animation is now handled by the theming layer, a looping animation
has been defined in the default CSS to handle active spinners.

This allows widgets to gtk_widget_set_state_flags() before mapping
and have animations started anyway when this happens.

gtk_icon_info_load_symbolic_for_style is going to be deprecated.