Added a Git .mailmap file

.mailmap

+Juergen Hoeller <jhoeller@vmware.com> jhoeller <jhoeller@vmware.com>
+<rstoyanchev@gopivotal.com> <rstoyanchev@vmware.com>
+<pwebb@gopivotal.com> <pwebb@vmware.com>
+<cbeams@gopivotal.com> <cbeams@vmware.com>
+<cbeams@gopivotal.com> <cbeams@gmail.com>
+<apoutsma@gopivotal.com> <apoutsma@vmware.com>
+<apoutsma@gopivotal.com> <poutsma@mac.com>
+<ogierke@gopivotal.com> <ogierke@vmware.com>
+<aclement@gopivotal.com> <david_syer@hotmail.com>
+<aclement@gopivotal.com> <andrew.clement@gmail.com>
+<aclement@gopivotal.com> <aclement@vmware.com>
+<dmitry.katsubo@gmail.com> <dmitry.katsubo@gmai.com>
+Nick Williams <nicholas@nicholaswilliams.net> Nicholas Williams <nicholas@nicholaswilliams.net>