Content update for -02

[mpiraux]

This MR propose two changes following recent feedback for the upcoming draft version:

• The YAML definitions have been replaced by CDDL
• A simple schema describe ground stations

[juanfraire]

Late to the party since this is merged, but for the record:

1. Units: the shell altitude is in kilometers while the ground-station altitude is in meters. Both are "above the Earth's surface", so this is an easy trap. I'd suggest harmonizing or making the unit part of the field name.
2. Epoch: the mean-anomaly reference epoch is still left to the simulation environment. Since reproducibility across tools is the document's stated goal, an optional epoch field in constellation-specs would close the largest remaining source of divergence (it also matters for ground stations, via Earth-rotation phase).
3. Indexing: the figures use [plane/rank], but the text never pins down which satellite is [0/0], the direction of plane numbering, or how phasing assigns ranks. Otherwise, two compliant tools can currently produce mirror-image topologies from the same document. A short normative paragraph would fix it.
4. Composability: one sentence making the central body an explicit parameter that defaults to Earth would keep the document exactly as it is for the LEO/ground case, while letting other documents compose it into interplanetary scenarios.

[mpiraux]

Hey, these are relevant still. I agree.

Regarding Indexing, it is very helpful as this is the kind of feedback that comes with people (other than me) trying to implement the document. I think we should have text (either in body either in appendix) that gives the formula for the phasing and seam effect. It's not well documented online last time I checked.

If we get very serious about it, some test vectors could be added to appendix as well.