Comm session re-architecture and self comm channel. (#145)

* Introduced self comm channel instead of loopback websocket.
* Introduced comm_session and comm_server inheritance hierarchy.
* Separated peer session and user session classes.

src/p2p/self_node.cpp

@@ -0,0 +1,28 @@
+#include "../pchheader.hpp"
+#include "peer_session_handler.hpp"
+
+namespace p2p::self
+{
+    // Holds self messages waiting to be processed.
+    moodycamel::ConcurrentQueue<std::string> msg_queue;
+
+    /**
+     * Processes the next queued message (if any).
+     * @return 0 if no messages in queue. 1 if message was processed successfully. -1 on error.
+     */
+    int process_next_message()
+    {
+        std::string msg;
+        if (msg_queue.try_dequeue(msg))
+            return p2p::handle_self_message(msg);
+
+        return 0;
+    }
+
+    void send(std::string_view message)
+    {
+        // Passing the ownership of message to the queue.
+        msg_queue.enqueue(std::string(message));
+    }
+
+} // namespace p2p::self