Incorporated ENet (reliable UDP protocol)

For maximum backwards compatibility, RoRnet version was bumped, SocketW is kept and server still listens for TCP connections on ip/port advertised on master server. Integration with master server is unchanged. Client version check is also unchanged. Only if client version matches, the server instructs the client to reconnect using ENet (using pre-existing unused RoRnet message MSG2_VERSION).

ENet communication is exactly the same as legacy TCP connection, with only one cosmetic detail - server info is sent to client using pre-existing unused RoRnet message MSG2_SERVER_SETTINGS rather than MSG2_HELLO. Server listens for ENet connections on the same IP as TCP and port+1.

This is a prototype done with minimum code changes, for easy understanding. Breakdown:
* listener.cpp (class Listner) - removed all TCP connection handling except version check and master server info query. Compatible clients are instructed to reconnect via ENet.
* dispatcher_enet.h/cpp (class DispatcherENet) - took over all connection handling logic from legacy Listener, except master server integration. Client version is checked again.
* sequencer.h/cpp (class User) - removed TCP socket and send/recv threads (classes Broadcaster, Receiver), deleted "FLOW mode" system ('m_is_receiving_data' flag and `SetReceiveData()` func - related to recv thrad). Added ENetPeer and DispatcherENet. Created function `MessageReceived()` which processes all incoming packets for this user, including intial HELLO.
* receiver.h/cpp (class Receiver) - deleted tcp recv thread, replaced by ENet.
* broadcaster.h/cpp (class Broadcaster) - deleted tcp send thread, replaced by ENet.
* sequencer.h/cpp (class Sequencer) - deleted killer thread and crash statistics, useless with ENet. Deleted "FLOW mode" system (function `enableFlow()` - related to send/recv threads). Function `createClient()` changed to `registerClient()` because the client object is now created early inside DispatcherENet.
* rorserver.cpp - use new DispatcherEnet, keep existing Listener

Author: ohlidalp

source/protocol/rornet.h

@@ -30,7 +30,7 @@ namespace RoRnet {
 #define RORNET_LAN_BROADCAST_PORT   13000  //!< port used to send the broadcast announcement in LAN mode
 #define RORNET_MAX_USERNAME_LEN     40     //!< port used to send the broadcast announcement in LAN mode
 
-#define RORNET_VERSION              "RoRnet_2.45"
+#define RORNET_VERSION              "RoRnet_2.50"
 
 enum MessageType
 {
@@ -44,7 +44,7 @@ enum MessageType
     MSG2_WELCOME,                      //!< we can proceed
 
     // Technical
-    MSG2_VERSION,                      //!< server responds with its version
+    MSG2_VERSION,                      //!< (repurposed) TCP only; instructs client to reconnect using ENet
     MSG2_SERVER_SETTINGS,              //!< server send client the terrain name: server_info_t
     MSG2_USER_INFO,                    //!< user data that is sent from the server to the clients
     MSG2_MASTERINFO,                   //!< master information response

source/server/CMakeLists.txt

@@ -5,6 +5,7 @@ add_executable(${PROJECT_NAME} ${server_src})
 
 target_include_directories(
         ${PROJECT_NAME} PRIVATE
+        ${CMAKE_SOURCE_DIR}/dependencies/enet/include
         ${CMAKE_SOURCE_DIR}/source/protocol/
         ${CMAKE_SOURCE_DIR}/source/common/
 )
@@ -20,10 +21,11 @@ if (RORSERVER_WITH_CURL)
     target_link_libraries(${PROJECT_NAME} PRIVATE CURL::libcurl)
 endif ()
 
-target_link_libraries(${PROJECT_NAME} PRIVATE Threads::Threads SocketW::SocketW jsoncpp_lib)
+target_link_libraries(${PROJECT_NAME} PRIVATE Threads::Threads SocketW::SocketW jsoncpp_lib enet)
 
 IF (WIN32)
     target_compile_definitions(${PROJECT_NAME} PRIVATE WIN32_LEAN_AND_MEAN NOMINMAX)
+    target_link_libraries(${PROJECT_NAME} PRIVATE winmm)
 ELSEIF (UNIX)
     #add_definitions("-DAS_MAX_PORTABILITY")
     target_link_libraries(${PROJECT_NAME} PRIVATE dl)