Create branch as in `git branch <branch_name> <start_point>`.

        If 'checkout' is True, checkout the branch after creation.

def branch(self, branch_name, start_point='HEAD', force=True,
               checkout=False):
        """Create branch as in `git branch <branch_name> <start_point>`.

        If 'checkout' is True, checkout the branch after creation.
        """
        return git_branch(
            self.repo_dir, branch_name, start_point, force=force,
            checkout=checkout)