Move wxAdv library contents into wxCore

This basically removes the "adv" library, even though it's still
preserved for compatibility with user make/project files referring to
it.

It is done because the distinction between "adv" and "core" was never
really clear (e.g. why wxTreeCtrl was in core but wxTreeListCtrl in
adv?) and it prevented some core classes from using adv ones.

docs/changes.txt

@@ -101,6 +101,8 @@ All:
 
 All (GUI):
 
+- wxAdvanced library was merged into wxCore, simply remove all references
+  to "adv" from your build system, it is not needed any longer.
 - Add wxDataViewToggleRenderer::ShowAsRadio().
 - Improve stock items consistency and aesthetics (dhowland).
 - Fix bug with missing items in overflowing AUI toolbar (Maarten Bent).