Node.js makes the full `ngtcp2_transport_params` struct available
for storage as a byte array, including any possible padding
in the struct.

Fully initializing the struct with `memset()` makes this deterministic.

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.

If `valuelen` is 0 and `p` equals `end`, decode_varint_param() reads an extra byte past the end of the buffer.

Remove transport parameter redundancy check because it causes now
segmentation fault.  The parameter type is now encoded in varint which
does not fit into 16 bits integer anymore.

It now defaults to 2 and includes CID exchanged during handshake.

The changed semantics will be implemented in the later commits.

Instead of installing key and iv with ngtcp2_conn_update_key, pass key
and iv buffers to ngtcp2_update_key and let application fill those
buffers.

This commit adds a static function named put_uint16_varint to reduce
some code duplication when putting some transport parameters.

This commit contains a suggestion to add a static function to reduce
some code duplication in ngtcp2_encode_transport_params.