[maint] Add git mailmap file

This deduplicates contributors in the git log.

[skip ci]

.mailmap

@@ -0,0 +1,21 @@
+# Prevent git from showing duplicate names with commands like "git shortlog"
+# See the manpage of git-shortlog for details.
+# The syntax is:
+# Name that should be used <email that should be used> Bad name <bad email>
+#
+# You can skip Bad name if it is the same as the one that should be used, and is unique.
+#
+# This file is up-to-date if the command git log --format="%aN <%aE>" | sort -u
+# gives no duplicates.
+Colin B. Macdonald <cbm@m.fsf.org> Colin Macdonald <macdonald@maths.ox.ac.uk>
+Colin B. Macdonald <cbm@m.fsf.org> Colin B. Macdonald <macdonald@maths.ox.ac.uk>
+Colin B. Macdonald <cbm@m.fsf.org> Colin Macdonald <cbm@m.fsf.org>
+Abhinav Tripathi <genuinelucifer@gmail.com> Abhinav <genuinelucifer@gmail.com>
+Abhinav Tripathi <genuinelucifer@gmail.com> <genuineabhinav@gmail.com>
+Carnë Draug <carandraug@octave.org> carandraug <devnull@localhost>
+Carnë Draug <carandraug@octave.org> <carandraug+dev@gmail.com>
+John W. Eaton <jwe@octave.org> jwe <devnull@localhost>
+Mike Miller <mtmiller@octave.org> <mtmiller@ieee.org>
+Andrés Prieto <prieto.aneiros@gmail.com> maprieto <prieto.aneiros@gmail.com>
+utkarsh <utkarshgautam247@gmail.com> utkarsh <iamutkash@cse.iitb.ac.in>
+