[ticket/12120] Add Marc Alexander to AUTHORS

PHPBB3-12120
Merge remote-tracking branch 'nickvergessen/ticket/12120' into develop-olympus

* nickvergessen/ticket/12120:
  [ticket/12120] Add Marc Alexander to AUTHORS
Merge branch 'develop-olympus' into develop-ascraeus

* develop-olympus:
  [ticket/12120] Add Marc Alexander to AUTHORS