Add definition and test for $.support.pjax property.

jquery.pjax/jquery.pjax-tests.ts

@@ -54,3 +54,7 @@ function test_defauluts() {
         version: $.noop
     };
 }
+
+function test_support() {
+    console.log($.support.pjax);
+}

jquery.pjax/jquery.pjax.d.ts

@@ -131,3 +131,10 @@ interface PjaxStatic {
      */
     reload(): JQueryXHR;
 }
+
+interface JQuerySupport {
+    /**
+     * A boolean value indicates if pjax is supported by the browser.
+     */
+    pjax: boolean;
+}