added .mailmap file

this is to properly connect variations of the same committer details to
the right identity

.mailmap

+Hallvard Trætteberg <hal@ntnu.no> Hallvard Trætteberg <hal@ntnu.no>
+Hallvard Trætteberg <hal@ntnu.no> Hallvard Traetteberg <hal@ntnu.no>
+Adrian Stoica <george.a.stoica@ntnu.no> Adrian Stoica <george.a.stoica@ntnu.no>  
+Adrian Stoica <george.a.stoica@ntnu.no> georgeas <george.a.stoica@ntnu.no>
+Adrian Stoica <george.a.stoica@ntnu.no> George Adrian Stoica <george.a.stoica@ntnu.no>
+Pål-Edward Larsen <paaledwl@stud.ntnu.no> Pål-Edward Larsen <paaledwl@stud.ntnu.no>
+Pål-Edward Larsen <paaledwl@stud.ntnu.no> paaledwl <paaledwl@stud.ntnu.no>