Add 'xo-callback/' from commit '4e1849c726'

git-subtree-dir: xo-callback
git-subtree-mainline: 42ee4bbdc2
git-subtree-split: 4e1849c726

xo-callback/src/callback/CallbackSet.cpp

@@ -0,0 +1,13 @@
+/* file CallbackSet.cpp
+ *
+ * author: Roland Conybeare, Sep 2022
+ */
+
+#include "CallbackSet.hpp"
+
+namespace xo {
+    namespace fn {
+    } /*namespace fn*/
+} /*namespace xo*/
+
+/* end CallbackSet.cpp */