Remove HTTP header aliases (API Change):

fix #382

* request_header and response_header are removed

include/beast/websocket/impl/accept.ipp

@@ -39,7 +39,7 @@ class stream<NextLayer>::response_op
     {
         bool cont;
         stream<NextLayer>& ws;
-        http::response_header res;
+        http::header<false, http::fields> res;
         int state = 0;
 
         template<class Fields, class Decorator>

include/beast/websocket/impl/stream.ipp

@@ -282,7 +282,7 @@ build_response(request_type const& req,
 template<class NextLayer>
 void
 stream<NextLayer>::
-do_response(http::response_header const& res,
+do_response(http::header<false> const& res,
     detail::sec_ws_key_type const& key, error_code& ec)
 {
     bool const success = [&]()