Add AUTHORS file

Thanks to
https://github.com/django-oscar/django-oscar/wiki/Releasing#contributors

AUTHORS

@@ -0,0 +1,28 @@
+David Winterbottom
+Maik Hoepfel
+Aymeric Augustin
+Izidor Matušov
+Julien Maupetit
+Zenobius Jiricek
+marco
+Skirmantas Jurgaitis
+Marco Fucci
+Miloud Belarbi
+Matthew Ghantous
+Caio Ariede
+Anentropic
+Alberto Bastos
+Adrian Fedoreanu
+suhail
+Steven Maggs
+Stefano Rago
+Sergey Maranchuk
+Sebastian Vetter
+Sean
+Pierre Dulac
+Moose
+Lex Berezhny
+joaoxsouls
+Filip Jukic
+armutcu
+Adam Charnock