Document and specify telemetry protocol

[jcward]

hxScout + HXT was modeled after Adobe Scout + FLM. That's all well and fine, but it grew (perhaps out of necessity) somewhat awkwardly with only a "make it work" specification.

It may be time for a review, a specification, perhaps an overhaul of the protocol, if it makes sense, as well as a CI setup and testcase-driven development.

We probably want this before / in tandem with new target support (e.g. HL.)