Add .mailmap

This allows for easy shortlog/log parsing, useful in determining
eligible members of the general assembly for the new FFmpeg voting
system.
Signed-off-by: Josh de Kock <josh@itanimul.li>

.mailmap

+<james.darnley@gmail.com> <jdarnley@obe.tv>
+<jeebjp@gmail.com> <jan.ekstrom@aminocom.com>
+<sw@jkqxz.net> <mrt@jkqxz.net>
+<u@pkh.me> <cboesch@gopro.com>
+<zhilizhao@tencent.com> <quinkblack@foxmail.com> <wantlamy@gmail.com>
+<modmaker@google.com> <modmaker-at-google.com@ffmpeg.org>
+<stebbins@jetheaddev.com> <jstebbins@jetheaddev.com>
+<barryjzhao@tencent.com> <mypopydev@gmail.com> <jun.zhao@intel.com>
+<josh@itanimul.li> <joshdk@obe.tv>
+<michael@niedermayer.cc> <michaelni@gmx.at>
+<linjie.fu@intel.com> <fulinjie@zju.edu.cn>
+<ceffmpeg@gmail.com> <cehoyos@ag.or.at>
+<ffmpeg@gyani.pro> <gyandoshi@gmail.com>
+<atomnuker@gmail.com> <rpehlivanov@obe.tv>
+<zhong.li@intel.com> <zhongli_dev@126.com>
+<andreas.rheinhardt@gmail.com> <andreas.rheinhardt@googlemail.com>