Add versions.md and version.h files describing version branches and tags #228

Having libmultiprocess version numbers should be helpful for:

• Backporting fixes for previous Bitcoin Core releases if we need to do that at some point (https://github.com/bitcoin/bitcoin/issues/33439).
• Letting Bitcoin Core releases describe what libmultiprocess versions they are compatible with (https://github.com/bitcoin/bitcoin/issues/33576)
• Letting code detect what version is used at compile-time or runtime, for logging, feature detection, error reporting, or other purposes.

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LLM Linter (✨ experimental)

Possible typos and grammar issues:

• include -> header [Sentence fragment: "Versioning policy is described in the version.h include." — "include" is awkward/incorrect here; "header" or "include file" makes the meaning clear.]

^{drahtbot_id_5_m}

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Updated 2b0dd9297529bde66d5b52efbde1a137013818e1 -> 6e01d2d766ebb6eb1fdc2136f5d39d93404c7e2a (pr/versions.1 -> pr/versions.2, compare)<!-- end --> fixing llm linter errors

ACK 6e01d2d766ebb6eb1fdc2136f5d39d93404c7e2a