Implement the '--format' option provided by 'ref-filter'. This lets the
user list branches as per desired format similar to the implementation
in 'git for-each-ref'.
Add tests and documentation for the same.
Mentored-by: Christian Couder <christian.couder@gmail.com> Mentored-by: Matthieu Moy <matthieu.moy@grenoble-inp.fr> Signed-off-by: Karthik Nayak <karthik.188@gmail.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>