Add .mailmap

Now git shortlog -ns has no duplicates. Also, I wanted an excuse to exercise
my push access :)

.mailmap

@@ -0,0 +1,12 @@
+# Prevent git from showing duplicate names with commands like "git shortlog"
+# See the manpage of git-shortlog for details.
+# The syntax is:
+# Name that should be used <email that should be used> Bad name <bad email>
+#
+# You can skip Bad name if it is the same as the one that should be used, and
+# is unique.
+#
+# This file is up-to-date if the command git log --format="%aN <%aE>" | sort
+# -u
+# gives no duplicates.
+Andreas Klöckner <inform@tiker.net> Andreas Kloeckner <inform@tiker.net