Add definition and test for $.pjax function.

jquery.pjax/jquery.pjax-tests.ts

@@ -8,6 +8,14 @@ function test_fn_pjax() {
     $(document).pjax("a", "#pjax-container", { push: true });
 }
 
+function test_pjax() {
+    $.pjax();
+    $.pjax({
+        url: "hello.html",
+        container: "#main"
+    });
+}
+
 function test_click() {
     var event = $.Event("click");
     $.pjax.click(event, "#pjax-container");

jquery.pjax/jquery.pjax.d.ts

@@ -58,6 +58,16 @@ interface JQueryStatic {
 }
 
 interface PjaxStatic {
+    /**
+     * Loads a URL with ajax, puts the response body inside a container, then pushState()'s the loaded URL.
+     * Works just like $.ajax in that it accepts a jQuery ajax settings object (with keys like url, type, data, etc).
+     * @param options PJAX settings, which is a superset of jQuery AJAX settings. It includes the following specific options:
+     * - container: a jQuery selector indicates where to stick the response body. E.g., $(container).html(xhr.responseBody).
+     * - push: a boolean indicates whether to pushState the URL. Default is true.
+     * - replace: a boolean indicates whether to use replaceState instead of pushState. Default is false.
+     */
+    (options?: PjaxSettings): JQueryXHR;
+
     /**
      * PJAX on click handler.
      * @param event A jQuery click event.