nghttpx: Use std::unique_ptr<char[]> instead of char*
nghttpx: Use nullptr instead of 0
nghttpx: Use std::vector for tls_proto_list and npn_list

Now SSL/TLS option mask to disable particular SSL/TLS protocol
versions are pre-calculated and stored in Config.
nghttpx: Code cleanup
nghttpx: Use nullptr instead of NULL
nghttpx: Code cleanup