Add mailmap file to normalize author names in git log

Avoid having entries differing just by name or email address (or, in the case
of Václav, by the use of composed vs decomposed form!) in "git shortlog"
output.

Closes https://github.com/wxWidgets/wxWidgets/pull/326

.mailmap

@@ -0,0 +1,29 @@
+ARATA Mizuki							<minorinoki@gmail.com>
+Artur Wieczorek							<artwik@wp.pl>
+Daniel Kulp		<dan@kulp.com>				<dkulp@apache.org>
+Bogdan Iordanescu						<bogdan_iordanescu@yahoo.com>
+Cătălin Răceanu							<maildus@gmail.com>
+			<maildus@gmail.com>			<catalinr@users.noreply.github.com>
+Dimitri Schoolwerth	<dimitri.schoolwerth@gmail.com>		<dimitri@schoolwerth.com>
+Hubert Talbot							<hubert.talbot64@gmail.com>
+Ilya Bizyaev							<bizyaev.game@yandex.ru>
+Jouk Jansen							<joukj@hrem.nano.tudelft.nl>
+Julian Smart							<julian@anthemion.co.uk>
+Kinaou Hervé							<kinaouherve@gmail.com>
+Lynn C. Rees							<lcrees@gmail.com>
+Maarten Bent							<MaartenBent@users.noreply.github.com>
+Manuel Martin							<mmartin@ceyd.es>
+Martin Ettl							<ettl.martin78@gmail.com>
+Micha Ahrweiler							<mbaschnitzi@users.noreply.github.com>
+Paul Cornett		<paulcor@bullseye.com>			<paulcor@users.noreply.github.com>
+Paul Kulchenko		<paul@kulchenko.com>			<paulclinger@gmail.com>
+Richard Fath							<richard.fath@t-online.de>
+Steve Browne		<swbrowne@gmail.com>			<sbrowne@unknown>
+Tim Kosse		<tim.kosse@gmx.de>			<tim.kosse@filezilla-project.org>
+Tobias Taschner		<ttaschner@protect-software.com>	<TcT2k@users.noreply.github.com>
+			<ttaschner@protect-software.com>	<github@tc84.de>
+Václav Slavík		<vaclav@slavik.io>			<vslavik@fastmail.fm>
+Václav Slavík							<vaclav@slavik.io>
+Vadim Zeitlin		<vadim@wxwidgets.org>			<vz-github@zeitlins.org>
+			<vadim@wxwidgets.org>			<vadim@zeitlins.org>
+Xlord2			<b1146285@trbvn.com>			<b1223723@trbvn.com>