ext/openssl/ossl_ssl.c (ossl_ssl_initialize): Added. Almost the same
as the Ruby version but this instantiate the SSL object at the same
time.
(ossl_ssl_setup): Adjust to the changes. Just set the underlying IO to
the SSL.
(ssl_started): Added. Make use of SSL_get_fd(). This returns -1 if not
yet set by SSL_set_fd().
(ossl_ssl_data_get_struct): Removed. Now GetSSL() checks that the SSL
exists.
(ossl_ssl_set_session): Don't call ossl_ssl_setup() here as now the
SSL is already instantiated in #initialize.
(ossl_ssl_shutdown, ossl_start_ssl, ossl_ssl_read_internal,
ossl_ssl_write_internal, ossl_ssl_stop, ossl_ssl_get_cert,
ossl_ssl_get_peer_cert, ossl_ssl_get_peer_cert_chain,
ossl_ssl_get_version, ossl_ssl_get_cipher, ossl_ssl_get_state,
ossl_ssl_pending, ossl_ssl_session_reused,
ossl_ssl_get_verify_result, ossl_ssl_get_client_ca_list,
ossl_ssl_npn_protocol, ossl_ssl_alpn_protocol, ossl_ssl_tmp_key): Use
GetSSL() instead of ossl_ssl_data_get_struct(). Use ssl_started().
(Init_ossl_ssl): Add method declarations of SSLSocket#{initialize,
hostname=}.