core: Implement websocket timeout in C.

src/http.h

@@ -210,6 +210,13 @@ const char* tf_http_get_cookie(const char* cookie_header, const char* name);
 */
 void tf_http_request_websocket_send(tf_http_request_t* request, int op_code, const void* data, size_t size);
 
+/**
+** Close a websocket.
+** @param request The HTTP request which was previously updated to a websocket
+** session with tf_http_request_websocket_upgrade().
+*/
+void tf_http_request_websocket_close(tf_http_request_t* request);
+
 /**
 ** Upgrade an HTTP request to a websocket session.
 ** @param request The HTTP request.