Protocol constraints - generic and per protocol level

[mlagally]

There were requests to clarify that the core profile is not exclusive for HTTP.

Consider defining protocol constraints that are common across different protocols in a common sectinon in chapter 4.2 and additionally have clarifications for individual protocols such as HTTP, MQTT etc.

For HTTP constraints we have enough knowledge from the Plugfests / POCs in the group.

Depending on contributions from the group we can include constraints for MQTT and other protocols.

[benfrancis]

The core/default profile must specify at least one protocol that all clients and servers must support in order to be conformant and ideally stick to a single protocol in order to reduce implementation complexity.

Trying to make a profile protocol agnostic will work against the goal of interoperability, not for it.

If there's a reason that some greenfield devices can't support the default profile (e.g. due to hardware constraints) then an additional profile could be created for a different protocol in future (e.g. CoAP). See #24

[benfrancis]

I think it's clear at this point that the Core Profile does require HTTP. I propose closing this issue.