Define wxDEBUG_LEVEL in both debug and release builds as 1.

By default include assertions and debug logging in both debug and release
builds but disable them in application release builds (when NDEBUG is
defined).

Also update (more accurately, replace) debugging overview.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@61886 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/common/appbase.cpp

@@ -1046,6 +1046,11 @@ wxDefaultAssertHandler(const wxString& file,
 
 wxAssertHandler_t wxTheAssertHandler = wxDefaultAssertHandler;
 
+void wxSetDefaultAssertHandler()
+{
+    wxTheAssertHandler = wxDefaultAssertHandler;
+}
+
 void wxOnAssert(const wxString& file,
                 int line,
                 const wxString& func,