Cleanup (to be broken into smaller issues)

[mmccool]

Some leftover points from Issue #209

• Should reference protocol bindings for other protocols rather than focusing on CoAP/HTTP/MQTT
• No mention of DID, SSI, other key distribution mechanisms
• End-to-end security mentions TD signing, but we have no good way to do that
• Protocol-specific comments in secure transport really about TLS/DTLS, which are a separate layer from protocols (e.g. can have OPC UA over these secure transports, too...)
• Need to refactor to figure what goes where in new charter; a lot of overlap with security and privacy considerations in other documents, lifecycle is out of place, etc.

[mmccool]

Probably some of these should be split out into more concrete issues and this one closed. I have assigned myself but just to do the reorganization into smaller issues.