ENH: fix developer names

Some developers are using several names in the commit. Some entries
are added in .mailcap to group the entries while using git shortlog.

Change-Id: I509277fee8b5a5512f72fb63bf07b279b2ffab85

.mailmap

@@ -3,3 +3,9 @@ Luis Ibanez <luis.ibanez@kitware.com>
 Hans Johnson <hans-johnson@uiowa.edu> <hans.j.johnson@gmail.com>
 Gaëtan Lehmann <gaetan.lehmann@jouy.inra.fr>
 Arnaud Gelas <arnaud_gelas@hms.harvard.edu>
+Alexandre Gouaillard <agouaillard@gmail.com>
+Andrew Wasem <drewwasem@gmail.com>
+Matthew McCormick <matt.mccormick@kitware.com>
+Matthew McCormick <matt@mmmccormick.com>
+Brian Avants <stnava@gmail.com>
+Nick Tustison <ntustison@gmail.com>