Add a .mailmap file

Among other things, this means that authors are identified
correctly in the output of "git shortlog".

.mailmap

@@ -0,0 +1,33 @@
+Anders Einar Hilden <hildenae@gmail.com>
+Andrew Perry <me@andrewperry.com.au>
+Anna Powell-Smith <annapowellsmith@gmail.com> <anna>
+Anna Powell-Smith <annapowellsmith@gmail.com> <annapowellsmith@gmail.com>
+bci-cities <bci-cities>
+Chris Lightfoot <chris@ex-parrot.com> <chris>
+Dave Whiteland <dave@mysociety.org> <dave@balti.ukcod.org.uk>
+Dave Whiteland <dave@mysociety.org> <dave@fury.ukcod.org.uk>
+Duncan Parkes <duncan@mysociety.org> <duncan@fury.ukcod.org.uk>
+Edmund von der Burg <evdb@mysociety.org> <evdb@ecclestoad.co.uk>
+Francis Irving <francis@mysociety.org> <francis>
+Guillaume Rischard <fixmystreet@stereo.lu> <fixmystreet@stereo.lu>
+Guillaume Rischard <fixmystreet@stereo.lu> <git@stereo.lu>
+Josh Angell <josh@supercooldesign.co.uk> <jbangell@gmail.com>
+Kagee <hildenae@gmail.com>
+Keith Garrett <keith@mysociety.org> <keith>
+Kevin Brubeck Unhammer <unhammer@fsfe.org>
+Louise Crow <louise@mysociety.org> <louise.crow@gmail.com>
+Louise Crow <louise@mysociety.org> <louise@peas.ukcod.org.uk>
+Louise Crow <louise@mysociety.org> <louise>
+Mark Longair <mark@mysociety.org> <mhl@pobox.com>
+Matthew Somerville <matthew@mysociety.org> <matthew>
+Matthew Somerville <matthew@mysociety.org> <matthew@balti.ukcod.org.uk>
+Matthew Somerville <matthew@mysociety.org> <matthew@cake.ukcod.org.uk>
+Matthew Somerville <matthew@mysociety.org> <matthew@dracos.co.uk>
+Matthew Somerville <matthew@mysociety.org> <matthew@fury.ukcod.org.uk>
+Matthew Somerville <matthew@mysociety.org> <matthew-github@dracos.co.uk>
+Matthew Somerville <matthew@mysociety.org> <matthew@mysociety.org>
+Matthew Somerville <matthew@mysociety.org> <matthew@rocket.ukcod.org.uk>
+Struan Donald <struan@mysociety.org> <struan@exo.org.uk>
+Struan Donald <struan@mysociety.org><struan@fury.ukcod.org.uk>
+Tim Morley <t_morley@argonet.co.uk> <timsk>
+Tony Bowden <tony@tmtm.com>