new IA2 landmark role

Hi Alex,

We changed the region role to be a subclass of ARIA landmarks. That manifests itself here:
http://rawgit.com/w3c/aria/master/core-aam/core-aam.html#role-map-region

Would you please add a role of landmark to IA2 to be equivalent tot he ATK/ATSPI role for landmark. So you would have 
role=“IA2_ROLE_LANDMARK”
Object attribute: xml-roles:region