Support Ruby-style version numbers

[perlun]

Sadly, Rubygems does not support Semantic Versioning. This means that you often use version strings like this:

• v1.0.0.beta.0
• v1.0.0.beta.1
• v1.0.0.beta.2
• v1.0.0.beta.3.1

..etc. Basically, it looks very similar to a SemVer string, but sadly, because of technical constraints, a proper SemVer prerelease version is not allowed as a Rubygems version identifier.

This is very unfortunate. However, it is life. It would be useful if changelog-rs would understand that these are in fact "valid SemVer prereleases". Probably by deducting that we have an "x.y.z.something" and convert that to a valid SemVer string or something... It is a kludge and a hack, but a useful hack.