[RFC] git tag last, shows the latest semver revision

Often enough I would like to know what is the latest tag number, but there are no simple commands e.g. `git tag last` or `git tag --last`

In git version >=2.0, there is now a `--sort="version:refname"` which could be helpful for this command:
```
       --sort=<type>
           Sort in a specific order. Supported type is "refname" (lexicographic order), "version:refname" or "v:refname" (tag names are treated as versions). Prepend "-" to reverse
           sort order.
```