add mailmap for contributors

.mailmap

@@ -0,0 +1,15 @@
+Ansgar Burchardt <ansgar@cpan.org> <ansgar@43-1.org>
+Christopher J. Madsen <cjm@cpan.org> <github@cjmweb.net>
+Christopher J. Madsen <cjm@cpan.org> <perl@cjmweb.net>
+Cory G Watson <gphat@cpan.org> <gphat@onemogin.com>
+Damyan Ivanov <dam@cpan.org> <dmn@debian.org>
+Eric Wilhelm <ewilhelm@cpan.org>
+Gregor Hermann <gregoa@debian.org>
+Ken Williams <kwilliams@cpan.org>
+Lars Dɪᴇᴄᴋᴏᴡ 迪拉斯 <daxim@cpan.org>
+Leon Timmermans <leont@cpan.org> <fawaka@gmail.com>
+Mark Fowler <markf@cpan.org> <mark@twoshortplanks.com>
+Michael G. Schwern <mschwern@cpan.org> <schwern@pobox.com>
+Randy Sims <randys@thepierianspring.org>
+Ricardo Signes <rjbs@cpan.org>
+Ævar Arnfjörð Bjarmason <avar@cpan.org> <avarab@gmail.com>