Allow definition of tag regexps to transform them according semver

Per repo config option ```tag-regexp``` in ```packages.json```

```
{"frontend/legacy": {
        "url": "git://github.com/some/repo.git",
        "minversion": "1.0",
        "tag-regexp": ["~^acme-(?P<major>\\d+)\\.(?P<minor>\\d+)\\.(?P<patch>\\d+)_(?P<pre-release>\\s+)#(?P<build>\\d+)~$"]
    }
}
```