Added subscription service capability.

Subscription.h

@@ -0,0 +1,32 @@
+#ifndef __Subscription_h__
+#define __Subscription_h__
+
+#include "TCPSession.h"
+#include "Command.h"
+#include "ZString.h"
+#include <vector>
+
+namespace core {
+
+   class Subscription : public Command {
+
+    public:
+      Subscription(std::string id, TCPSession &session);
+
+      int subscribe(TCPSession &session);
+      int unsubscribe(TCPSession &session);
+      virtual int process(coreutils::ZString &request, std::stringstream &out);
+
+      int event(std::stringstream &out);
+
+      int processCommand(coreutils::ZString &request, TCPSession &session) override;
+
+      std::string id;
+      TCPSession *owner;
+
+      std::vector<TCPSession *> subscribers;
+
+   };
+}
+
+#endif