Implement local notification.

The default behavior is to only notify remote changes, but for some
applications (e.g. GUI's) it's advantageous to know about local
changes as well.

This is (slightly) optimized in that local changes only result in
additional resources being consumed if (any) local listeners have been
created.

src/ntcore_c.cpp

@@ -169,14 +169,15 @@ void NT_Flush(void) { nt::Flush(); }
 unsigned int NT_AddEntryListener(const char *prefix, size_t prefix_len,
                                  void *data,
                                  NT_EntryListenerCallback callback,
-                                 int immediate_notify) {
+                                 int immediate_notify, int local_notify) {
   return nt::AddEntryListener(
       StringRef(prefix, prefix_len),
       [=](unsigned int uid, StringRef name, std::shared_ptr<Value> value,
           bool is_new) {
         callback(uid, data, name.data(), name.size(), &value->value(), is_new);
       },
-      immediate_notify != 0);
+      immediate_notify != 0,
+      local_notify != 0);
 }
 
 void NT_RemoveEntryListener(unsigned int entry_listener_uid) {