IE8 and 9 support added

Old IE browsers use ActiveXObject instead of XMLHttpRequest, so this is added for plain Ajax. The API is also adapted to handle different phases of the Ajax call specific to ActiveXObject.

IE8 and IE9 support CORS, but not with XMLHttpRequest object, but with an IE specific XDomainRequest. While this has some limitations, it supports plain GET requests without custom headers, which could fit some user's needs. It has some specific functions which were also incorporated in this update.