Merge branch 'sg/config-name-only'

"git config --list" output was hard to parse when values consist of multiple lines. "--name-only" option is added to help this. * sg/config-name-only: get_urlmatch: avoid useless strbuf write format_config: simplify buffer handling format_config: don't init strbuf config: restructure format_config() for better control flow completion: list variable names reliably with 'git config --name-only' config: add '--name-only' option to list only variable names