* Per-signal `timestamp` due to the nature of USS signals.
* Keeping `message`->`timestamp` so any Listener relying on it being there
isn't tripped up (it's present in all other schemas).
* Specifiy that each `signals` member should have `event` key/value pair
removed.
* Mandate removal of `SystemAddress` from each `signals` member.
* Receivers: Only `horizons` and `odyssey` augmentations are optional.
* Updated examples for these changes.
* Purely event-based batching, no timer.
* Outline Horizons/Odyssey differences.
* Point out that USS are manually scanned, so different in time nature.
* StarSystem renamed from systemName.
* StarSystem and StarPos now mandatory.