Add author mappins for the git log

See https://git-scm.com/docs/git-shortlog#_mapping_authors

Makes for a prettier commit overview:
$ git shortlog -s -n --no-merges
  1673  Juan Linietsky
   696  Rémi Verschelde
   239  volzhs
   225  Andreas Haas
   209  Ignacio Etcheverry
   164  Daniel J. Ramirez
   164  Pedro J. Estébanez
   153  George Marques
   150  Paul Batty
   129  Poommetee Ketson
   122  Franklin Sobrinho
   120  marynate
   115  Bojidar Marinov
   107  Leon Krause
    96  Thomas Herzog
   ...

.mailmap

@@ -0,0 +1,26 @@
+Andrea Catania <[email protected]>
+Andreas Haas <[email protected]>
+Andreas Haas <[email protected]>
+Andreas Haas <[email protected]>
+Ariel Manzur <[email protected]>
+Ariel Manzur <[email protected]>
+Bastiaan Olij <[email protected]>
+Bernhard Liebl <[email protected]>
+Bernhard Liebl <[email protected]>
+Geequlim <[email protected]>
+Ignacio Etcheverry <[email protected]>
+Indah Sylvia <[email protected]>
+Jakub Grzesik <[email protected]>
+Juan Linietsky <[email protected]>
+Juan Linietsky <[email protected]>
+Juan Linietsky <[email protected]>
+Julian Murgia <[email protected]>
+Leon Krause <[email protected]>
+Leon Krause <[email protected]> <[email protected]>
+Marcelo Fernandez <[email protected]>
+Mariano Javier Suligoy <[email protected]>
+Paul Batty <[email protected]>
+Poommetee Ketson <[email protected]>
+Saracen <[email protected]>
+Thomas Herzog <[email protected]>
+Zher Huei Lee <[email protected]>