IE9 CORS not supported

[ChrisBAshton]

I get a SCRIPT 5: Access is denied error message in IE9 when using Pegasus to ajax in some JSON over a different origin.

Managed to fix by polyfilling XHR with xhook and providing a before hook as per http://jpillora.com/xhook/example/ie-8-9-cors-polyfill.html

Appreciate that adding support for CORS in IE9 adds a lot of extra bloat. I suggest we add something to the README to make it clear that IE9 ajax requests are supported, just not over CORS?