switch to coroutine execution model

src/ServerShell.hh

@@ -3,9 +3,6 @@
 #include <memory>
 #include <string>
 
-#include <event2/event.h>
-
-#include "ProxyServer.hh"
 #include "ServerState.hh"
 
 class ServerShell : public std::enable_shared_from_this<ServerShell> {
@@ -17,8 +14,6 @@ public:
   ServerShell& operator=(ServerShell&&) = delete;
   ~ServerShell();
 
-  std::shared_ptr<ProxyServer::LinkedSession> get_proxy_session(const std::string& name);
-
 protected:
   std::shared_ptr<ServerState> state;
   std::thread th;