Change Padding packet to Non-Critical packet
- change the Padding packet to a generic "Non-Critical" packet type with a "padding" subpacket.
- require parsers to be strict with remaining unknown packet types
Closes: #121 (closed)
This is one opinionated way to address #121 (closed). I would be happy to compare/contrast this against a different MR that proposes an explicitly lenient packet sequence grammar.