the change, the demo was always sending packets bound for V4 through the
V6 socket, and they were lost!

Added unittest for erroneous transport parameters, verify that connection is closed with adequate error.

Added the possibility to emit and receive connection close messages during the initial handshake. This can be triggered in particular when encountering a transport parameter error.

Make sure that all the connection tests work, with both the new version and the old bidir only version.

Updated the version parameter encoding to new format and new parameters. Fixed missing fields in rarely used frames.

Updated transport parameter encoding to new format, including new unidir and ack delay exponent parameters.

Applied "invariant" change that sets the version number to zero in negotiation packet, and redefines the packet types.

packet header encoding.

Implemented the new packet header format, with version dependent parsing. Updated the tests, verified that every test pass.

Fixed compilation warnings.

Debugged the issue that caused picoquicdemo to fail when the initial command line was fragmented.
Debugged a number of issues in the encoding of frames with varint.

Fixed bug in closing sequence. Now ensures that the peer sends a connection_close in response to a received closing message.

Fixing bugs found by skip frames unit test. Also, make sure the unit test will work for Linux builds.