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 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.

Remove NGTCP2_ALPN_H3 macro which should be defined by HTTP/3 layer.

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.

Until mainline support of QUIC are present in OpenSSL and GnuTLS, be
sure to test whether the found library versions are the patched ones
since the version number check is insufficient. This fixes the default
build on a system where a new GnuTLS is present without the patches from
the GnuTLS tmp-quic branch.

Add new ENABLE_OPENSSL and ENABLE_GNUTLS CMake options to allow
explicitly disabling these libraries to mirror the --without-openssl and
the --without-gnutls functionality of autotools.

Partially addresses https://github.com/ngtcp2/ngtcp2/issues/238