If OpenSSL supports TLSv1.3, enable it by default for all applications
under src. BoringSSL can work at the moment although it does not
unlock all the features nghttpx offers. OpenSSL's TLSv1.3 support is
still WIP at the time of writing.
Compile with BoringSSL except for neverbleed and libnghttp2_asio. The
former uses ENGINE and RSA_METHOD, and they are quite different
between OpenSSL and BoringSSL. The latter uses boost::asio, which
calls OpenSSL functions deleted in BoringSSL.
This commit add following 3 log variables to SSL/TLS connection:
$ssl_cipher, $ssl_protocol, $ssl_session_id. If no information is
available for them, '-' is produced for each.
Tatsuhiro Tsujikawa