Changes with nginx 1.13.0 25 Apr 2017
*) Change: SSL renegotiation is now allowed on backend connections.
*) Feature: the "rcvbuf" and "sndbuf" parameters of the "listen" directives of the mail proxy and stream modules.
*) Feature: the "return" and "error_page" directives can now be used to return 308 redirections. Thanks to Simon Leblanc.
*) Feature: the "TLSv1.3" parameter of the "ssl_protocols" directive.
*) Feature: when logging signals nginx now logs PID of the process which sent the signal.
*) Bugfix: in memory allocation error handling.
*) Bugfix: if a server in the stream module listened on a wildcard address, the source address of a response UDP datagram could differ from the original datagram destination address.