Add documentation for ajaxSetup() and xhrFields

Author: morganheimbeck

can-ajax.js

@@ -36,9 +36,31 @@ var param = require("can-param");
  *      - __data__ `{Object}` The data of the request. If data needs to be urlencoded (e.g. for GET requests or for CORS) it is serialized with [can-param].
  *      - __dataType__ `{String}` Type of data. _Default is `json`_.
  *      - __crossDomain__ `{Boolean}` If you wish to force a crossDomain request (such as JSONP) on the same domain, set the value of crossDomain to true. This allows, for example, server-side redirection to another domain. Default: `false` for same-domain requests, `true` for cross-domain requests.
- *
+ *	- __xhrFields__ `{Object}` Any fields to be set directly on the xhr request, [https://developer.mozilla.org/en-US/docs/Web/API/XMLHttpRequest] such as the withCredentials attribute that indicates whether or not cross-site Access-Control requests should be made using credentials such as cookies or authorization headers.
+ *	
  *    @return {Promise} A Promise that resolves to the data. The Promise instance is abortable and exposes an `abort` method. Invoking abort on the Promise instance indirectly rejects it.
  *
+ *
+ * @signature `ajaxSetup( ajaxOptions )`
+ *
+ *    Is used to persist ajaxOptions across all ajax requests and they can be over-written in the ajaxOptions of the actual request. 
+ *    [https://api.jquery.com/jquery.ajaxsetup/]
+ *
+ *    ```
+ *    var ajax = require("can-ajax");
+ *
+ *    ajax.ajaxSetup({xhrFields: {withCredentials: true}});
+ *
+ *    ajax({
+ *      url: "http://query.yahooapis.com/v1/public/yql",
+ *      data: {
+ *        format: "json",
+ *        q: 'select * from geo.places where text="sunnyvale, ca"'
+ *      }
+ *    }).then(function(response){
+ *      console.log( response.query.count ); // => 2
+ *    });
+ *    ```
  */
 
 // from https://gist.github.com/mythz/1334560
@@ -202,11 +224,11 @@ function ajax(o) {
 		xhr.setRequestHeader("X-Requested-With", "XMLHttpRequest");
 	}
 
-    if (o.xhrFields) {
-        for (var f in o.xhrFields) {
-            xhr[f] = o.xhrFields[f];
+        if (o.xhrFields) {
+            for (var f in o.xhrFields) {
+                xhr[f] = o.xhrFields[f];
+            }
         }
-    }
 
 	xhr.send(data);
 	return promise;