[gtk] (10 commits) ...Merge branch 'wip/otte/symbolic-paintable' into 'master'

[Benjamin Otte <otte src gnome org>]

Summary of changes:

  2f9a67b... docs: Fix vfunc references (*)
  36dd959... build: Check that introspection is enabled for docs build (*)
  49d109c... gtk: Add the GtkSymbolicPaintable interface (*)
  2808f9c... gtk: Port icontheme to GtkSymbolicPaintable (*)
  1b390d3... gtk-demo: Explicitly pass nuclear icon colors (*)
  7cdbdb6... gtk-demo: Add a symbolic paintable demo (*)
  6c87d36... enums: Add a GtkSymbolicColor enum (*)
  9237c8b... icontheme: Refactor gtk_icon_theme_lookup_symbolic_colors() (*)
  91d1ec4... symbolicpaintable: Refactor default colors path (*)
  3b15f32... Merge branch 'wip/otte/symbolic-paintable' into 'master'

(*) This commit already existed in another branch; no separate mail sent