Feature/httpd (#94)

* Stub code for http server

* can send a response, cannot process body yet

* write headers to the response

* remove commented code

* add simple test + set default http handler

* tweak CI + unittest

* add missing file

* rewrite http::trim in a simple way

* doc

test/IXTest.h

@@ -8,6 +8,7 @@
 
 #include <iostream>
 #include <ixwebsocket/IXWebSocketServer.h>
+#include "IXGetFreePort.h"
 #include <mutex>
 #include <spdlog/spdlog.h>
 #include <sstream>
@@ -46,7 +47,5 @@ namespace ix
 
     void log(const std::string& msg);
 
-    int getFreePort();
-
     bool startWebSocketEchoServer(ix::WebSocketServer& server);
 } // namespace ix