SemVer: allow PreRelease containing digits, and without a version

[BoD]

Noticed that using Kotlin 2.4.0-Beta2 would throw when configuring BCV, even though it is a valid SemVer version.

(Unfortunately ABI breaking, hopefully not a big deal.)

(Of course this would be avoided if JetBrains were naming their version 2.4.0-beta.2 as God intended 😂)

[martinbonnin]

Thanks for the pull request! I'd like this SemVer class to be quite strict about what it supports and keep it for versions we have control over.

For Kotlin version, I switched to using lexicographical sorting in #128, let me know how that works for you!

[BoD]

Works for me!