core: drop std::function and ndn::Exclude from common.hpp, add ndn::optional

Change-Id: Ie3983d8b6f9929430efd8ada8d942e3f95755cd4
diff --git a/tools/nfdc/forwarder-general-module.cpp b/tools/nfdc/forwarder-general-module.cpp
index 67093ec..e0d6b1b 100644
--- a/tools/nfdc/forwarder-general-module.cpp
+++ b/tools/nfdc/forwarder-general-module.cpp
@@ -34,7 +34,7 @@
 
 void
 ForwarderGeneralModule::fetchStatus(Controller& controller,
-                                    const function<void()>& onSuccess,
+                                    const std::function<void()>& onSuccess,
                                     const Controller::DatasetFailCallback& onFailure,
                                     const CommandOptions& options)
 {