Pass struct sockaddr to ngtcp2 so that it knows how to deal with
address change in more detailed manner (e.g., just compare IP address
without port).

This commit fixes the assertion failure which happens when
acknowledgement of earlier packet increases CRYPTO offset.
Previously, the offset is always the first CRYPTO frame offset in the
queue (pktns->crypto.tx.frq).  But passing this into
ngtcp2_pkt_crypto_max_datalen() underestimates the space because
acknowledgement might increase offset; it increases the required space
to serialize offset.

This commit introduces ngtcp2_stream_data_flags.  The signature of
ngtcp2_recv_stream_data is reworked.  More specifically, flags
parameter is added.  The fin parameter is removed and it is replaced
with NGTCP2_STREAM_DATA_FLAG_FIN flag.  NGTCP2_STREAM_DATA_FLAG_0RTT
flag is added to indicate that the data might be replayed.

Deal with initial_scid, retry_scid, and original_dcid.  We need to set
and get QUIC transport parameters timely manner.  Therefore, transport
parameter operations are now done by ngtcp2_crypto library.
Applications do not need to do set it manually.  Added several
callback function implementations to ngtcp2_crypto library which can
be directly passed to ngtcp2_callbacks: client_initial, recv_retry,
and recv_client_initial.  Installation of initial packet number space
encryption keys is now handled by ngtcp2_crypto library.  They are
done in ngtcp2_crypto_client_initial_cb, ngtcp2_crypto_recv_retry_cb
and ngtcp2_crypto_recv_client_initial_cb.

Round up cwnd left to the maximum UDP packet size to avoid small
packet.

This commit separates key installation function into 2 and let TLS
stack install rx and tx keys separately for handshake and 1RTT keys.
This change is aligned to the new BoringSSL API and GnuTLS API.  I
expect that OpenSSL will follow this change.  It also removes side
argument from crypto API if it can be inferred by
ngtcp2_conn_is_server.

Fixes #224