Add .mailmap, mapping Git committers and authors to canonical names.

.mailmap

@@ -0,0 +1,13 @@
+Aaron Bentley <abentley@panoramicfeedback.com> <aaron.bentley@utoronto.ca>
+Ben Finney <benf@cybersource.com.au> <ben+python@benfinney.id.au>
+Ben Finney <benf@cybersource.com.au> <jdoe@example.com>
+Chris Ball <cjb@laptop.org> <cjb@t60>
+Chris Ball <cjb@laptop.org> <cjb@thunk.printf.net>
+Gianluca Montecchi <gian@grys.it>
+Gianluca Montecchi <gian@grys.it> <gian@galactica>
+Gianluca Montecchi <gian@grys.it> <gian@li82-39>
+Jan Gerber <j@oil21.org>
+Marien Zwart <marien.zwart@gmail.com> <marienz@gentoo.org>
+Tanguy Le Carrour <tanguy.lecarrour@gmail.com>
+W. Trevor King <wking@drexel.edu> <wking@thialfi>
+W. Trevor King <wking@drexel.edu> <wking@mjolnir>