Method rename

src/chain.rs:356–370

(self, git_chain: &GitChain, new_chain_name: &str)

    }

    pub fn rename(self, git_chain: &GitChain, new_chain_name: &str) -> Result<(), Error> {
        // invariant: new_chain_name chain does not exist
        assert!(!Chain::chain_exists(git_chain, new_chain_name)?);

        for branch in self.branches {
            Branch::setup_branch(
                git_chain,
                new_chain_name,
                &branch.root_branch,
                &branch.branch_name,
                &SortBranch::Last,
            )?;
        }
        Ok(())
    }
}