"git format-patch --commit-list-format" enables the user to make their
own format for the commit list in the cover letter. It would be nice to
have a ready to use format to replace shortlog.
Teach make_cover_letter() the "modern" format preset.
This new format is the same as: "log:[%(count)/%(total)] %s".
Signed-off-by: Mirko Faina <mroik@delayed.space>
Signed-off-by: Junio C Hamano <gitster@pobox.com>