Enhancements - shadow file

- Implemented (bug not debugged) the shadow file update.
- Added oddly missing (and bypassed) Context::message and Context::footnote
  methods.

src/Context.h

@@ -47,7 +47,7 @@ public:
   void initialize ();                  // for reinitializing
   int run ();                          // task classic
   int interactive ();                  // task interactive (not implemented)
-  void dispatch ();                    // command handler dispatch
+  std::string dispatch ();             // command handler dispatch
   void shadow ();                      // shadow file update
 
   int getWidth ();                     // determine terminal width