Add definition and test for $.pjax.reload method.

jquery.pjax/jquery.pjax-tests.ts

@@ -37,3 +37,7 @@ function test_enable() {
 function test_disable() {
     $.pjax.disable();
 }
+
+function test_reload() {
+    $.pjax.reload();
+}

jquery.pjax/jquery.pjax.d.ts

@@ -120,4 +120,9 @@ interface PjaxStatic {
      * This is the case when a browser doesn't support pushState. It is sometimes useful to disable pushState for debugging on a modern browser.
      */
     disable(): void;
+
+    /**
+     * Reload current page with pjax.
+     */
+    reload(): JQueryXHR;
 }