:return: List of Versions for this Item

def versions(self, rev=None, index=None):
        """:return: List of Versions for this Item"""
        raise NotImplementedError
        _revisions = [line.split()[0] for line in self.log.split('\n') if line]
        _versions = [Version(self.obj.repo.commit(r)) for r in _revisions if rev is None or r.startswith(rev)]
        if index is not None and len(_versions) > index:
            _versions = _versions[index]
        return _versions