Docs: Missing documentation that `['*', 'x', 'X']` can all be wildcards

[nyurik]

By accident, I discovered that VersionReq can parse all 3 of ['*', 'x', 'X'] characters as a wildcard, while it is not documented either here nor in cargo rust docs. Are there any difference between how they are used?

https://github.com/dtolnay/semver/blob/4ea60ae121bf0c8c5ad7e7aa5a9f663f305b7400/src/parse.rs#L191-L201

[andrius-puksta-sensmetry]

*, x and X are treated exactly the same. This was added in https://github.com/dtolnay/semver/pull/247 to match cargo's previous behavior.