Modify item data and commit to repo. 
        Git objects are immutable, to save means adding a new item

        :param msg: Commit message.

def save(self, msg=None):
        """
        Modify item data and commit to repo. 
        Git objects are immutable, to save means adding a new item

        :param msg: Commit message.
        """
        if msg is None:
            msg = 'Saving %s' % self.name
        log.debug(msg)
        self.repo.addItem(self, msg)