git-multimail: update to release 1.5.0

git-multimail: update to release 1.5.0

Changes are described in CHANGES.

Contributions-by: Matthieu Moy <git@matthieu-moy.fr>
Contributions-by: William Stewart <william.stewart@booking.com>
Contributions-by: Ville Skyttä <ville.skytta@iki.fi>
Contributions-by: Dirk Olmes <dirk.olmes@codedo.de>
Contributions-by: Björn Kautler <Bjoern@Kautler.net>
Contributions-by: Konstantin Ryabitsev <konstantin@linuxfoundation.org>
Contributions-by: Gareth Pye <garethp@gpsatsys.com.au>
Contributions-by: David Lazar <lazard@csail.mit.edu>
Signed-off-by: Matthieu Moy <git@matthieu-moy.fr>
Signed-off-by: Junio C Hamano <gitster@pobox.com>