Encoding and decoding of snapshot metadata as CBOR

[jorisdral]

No description provided.

[mheinzel]

Looks reasonable, but maybe @dcoutts should also take a quick look.

[dcoutts]

The explanation of major/minor has gone after the rebase. I was drafting an alternative.

I think the precision doesn't really aid comprehension here. How about:

-- A snapshot format version @x.y@ has two components: a major version number
-- @x@ and a minor version number @y@. The major version number is used to
-- signal breaking changes and the minor version number is used to signal
-- non-breaking changes.
--
-- A single release of the library may support several major snapshot format
-- versions, and thereby provide backwards compatibility. Support for old
-- major versions is not guaranteed indefinitely however. Forwards
-- compatibility is not provided at all: snapshots with a later major version
-- than the current version for the library release will always fail.
--
-- The minor version has no influence on whether a snapshot can be loaded or not:
-- minor version format changes are always compatible. They may however have an
-- effect, since later minor versions may have more information, that
-- corresponding releases can decode. These effects will never affect functional
-- correctness.

[jorisdral]

@dcoutts done

[mheinzel]

I think that's better 👍

[mheinzel]

A simpler way of saying this would be "a snapshot format version is a number", maybe also mentioning they're consecutive and increasing?

[mheinzel]

Suggested change

	-- is not provided at all: snapshots with a later major version than the current
	-- version for the library release will always fail.
	-- is not provided at all: snapshots with a later version than the current
	-- version for the library release will always fail.

[dcoutts]

Looking good!