Add .mailmap to normalize committer names

Author: zonuexe

.mailmap

@@ -0,0 +1,6 @@
+Elis Axelsson <elis.axelsson@gmail.com> Elis <elis.axelsson@gmail.com>
+David Arroyo Menéndez <davidam@gnu.org> David Arroyo7 <davidam@gnu.org>
+Joe Wreschnig <joe.wreschnig@gmail.com> Joe <joe@dev3>
+Jon Dufresne <jon.dufresne@gmail.com> Jon Dufrense <mailto:jon.dufresne@gmail.com>
+Syohei YOSHIDA <syohex@gmail.com> Shohei YOSHIDA <shohei.yoshida@dena.com>
+Syohei YOSHIDA <syohex@gmail.com> Syohei Yoshida <syohex@gmail.com>