Add CalVer support

[Kjarrigan]

For some applications especially the web-apps SemVer isn't really a good pick so supporting something like
https://calver.org/ would be nice. The lib suggest that this was meant to be changeable?

The site describes various options but I think for our use-case sticking to one defined type is sufficient. Something like

YYYY.0M.0D[.HOTFIX]