All colors are defined now in the default css, and classes have
been added so the bars are fully themeable (as opposed to
gtk_widget_override_*, which require changing the color map itself)

Coordinates needed to be translated relative to the window position
in within the widget.

I committed my whole working tee instead of just one file. Ooops.
This reverts commit ded14b25.

It was accidentally removed in 0775b0a8

and deprecate gtk_icon_set_render_icon().

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

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

This function replaces gtk_style_set_background().

This function is similar to gtk_style_render_icon(), which is now
implemented on top of this one.

This method will render progress bars and spinners, these should
handle active and inconsistent states' animation progress in order
to perform animations.

Several classes and regions may be set to GtkStyleContext, so rename
the functions to be more intuitive.

It actually messed up with the state being actually set, and having a
transition animation running for it. Now this dichotomy is removed, and
gtk_style_context_state_is_running() only checks whether an animation is
running, leaving state checking to flags & GTK_STATE_FLAG_*.

Both API and file format is documented, there's still missing
a migration doc though.

The case for paned can be guessed out from the height and width,
for handlebox the orientation parameter doesn't make much sense,
and this way it could also be used for resize grips.

Invalidation region coalescing now happens recursively as draw() runs, and the
widget's x/y as now drawing coordinates are 0,0 based.

This function recalculates the style for all widgets on a screen.

These functions allow per-screen style providers. also, the changed signal
will be emitted whenever a style context changes.

This function will regenerate all styling information.

Animation regions are confined through gtk_style_context_[push|pop]_animatable_region,
anything that's painted between these calls will be invalidated if an animation starts
for any of the regions in the stack.

gtk_style_context_notify_state_change() may be called from widgets to indicate a
change for a given GtkStateType, in that case an animation will be started if there
is an animation description for the widget/state.

This support goes from the theming engines, which are able to retrieve
style for different combined states to the CSS provider, where several
state pseudo-classes may be specified, such as:

GtkButton:active:prelight {}

"Child class" is an invented term anyway, and it conceptually defines
identifiable regions in widgets.

These functions will help widgets specify how does one element being painted
relate to other contiguous elements.

gtk_style_lookup_color() now uses this function internally.