git-multimail: update to version 1.0.0

This commit contains the squashed changes from the upstream
git-multimail repository since the last code drop.  Highlights:

* Fix encoding of non-ASCII email addresses in email headers.

* Fix backwards-compatibility bugs for older Python 2.x versions.

* Fix a backwards-compatibility bug for Git 1.7.1.

* Add an option commitDiffOpts to customize logs for revisions.

* Pass "-oi" to sendmail by default to prevent premature
  termination
  on a line containing only ".".

* Stagger email "Date:" values in an attempt to help mail clients
  thread the emails in the right order.

* If a mailing list setting is missing, just skip sending the
  corresponding email (with a warning) instead of failing.

* Add a X-Git-Host header that can be used for email filtering.

* Allow the sender's fully-qualified domain name to be configured.

* Minor documentation improvements.

* Add a CHANGES file.

Contributions-by: Raphaël Hertzog <hertzog@debian.org>
Contributions-by: Eric Berberich <eric.berberich@gmail.com>
Contributions-by: Michiel Holtkamp <git@elfstone.nl>
Contributions-by: Malte Swart <mswart@devtation.de>
Signed-off-by: Michael Haggerty <mhagger@alum.mit.edu>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Merge branch 'mh/multimail' into next

* mh/multimail:
  git-multimail: update to version 1.0.0