Add '.mailmap'.

* .mailmap: New file.

.mailmap

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+# This list is used to avoid multiple name/email instances of the same
+# contributors reported by "git log" and "git shortlog" commands.
+
+Alexander I. Grafov <grafov@gmail.com>
+Amirouche Boubekki <amirouche@hypermove.net>
+Ben Woodcroft <b.woodcroft@uq.edu.au> <donttrustben@gmail.com>
+Claes Wallin (韋嘉誠) <claes.wallin@greatsinodevelopment.com>
+Cyprien Nicolas <cyprien@nicolas.tf> <c.nicolas+gitorious@gmail.com>
+David Thompson <davet@gnu.org> <dthompson2@worcester.edu>
+David Thompson <davet@gnu.org> <dthompson@member.fsf.org>
+Deck Pickard <deck.r.pickard@gmail.com> <nebu@kipple>
+Eric Bavier <bavier@member.fsf.org> <ericbavier@gmail.com>
+John Darrington <jmd@gnu.org> <john@darrington.wattle.id.au>
+Joshua Grant <tadni@riseup.net> <gzg@riseup.net>
+Joshua Grant <tadni@riseup.net> <jgrant@parenthetical.io>
+Joshua Grant <tadni@riseup.net> <tadnimi@gmail.com>
+Joshua Grant <tadni@riseup.net> <youlysses@riseup.net>
+Ludovic Courtès <ludo@gnu.org> <ludovic.courtes@inria.fr>
+Mathieu Lirzin <mthl@openmailbox.org> <mathieu.lirzin@openmailbox.org>
+Nikita Karetnikov <nikita@karetnikov.org> <nikita.karetnikov@gmail.com>
+Pjotr Prins <pjotr.public01@thebird.nl>
+Pjotr Prins <pjotr.public01@thebird.nl> <pjotr.public12@thebird.nl>
+Ricardo Wurmus <rekado@elephly.net>
+Ricardo Wurmus <rekado@elephly.net> <ricardo.wurmus@mdc-berlin.de>
+Sou Bunnbu (宋文武) <iyzsong@gmail.com>
+Taylan Ulrich Bayırlı/Kammer <taylanbayirli@gmail.com>
+Tomáš Čech <sleep_walker@gnu.org> <sleep_walker@suse.cz>