Added val methods

- ref https://github.com/twitter/typeahead.js/blob/master/doc/jquery_typeahead.md#api

typeahead/typeahead-tests.ts

@@ -85,3 +85,8 @@ $('.example-countries .typeahead').typeahead({
   prefetch: '../data/countries.json',
   limit: 10
 });
+
+module valueTest {
+    var value: string = $('foo').typeahead('val');
+    $('foo').typeahead('val', value);
+}

typeahead/typeahead.d.ts

@@ -60,6 +60,17 @@ interface JQuery {
       * @param dataset Array of datasets
       */
     typeahead(options: Twitter.Typeahead.Options, dataset: Twitter.Typeahead.Dataset): JQuery;
+
+    /**
+      * Returns the current value of the typeahead. The value is the text the user has entered into the input element.
+      */
+    typeahead(methodName: 'val'): string;
+    typeahead(methodName: string): string;
+
+    /**
+      * Sets the value of the typeahead. This should be used in place of jQuery#val.
+      */
+    typeahead(methodName: 'val', value: string): JQuery;
 }
 
 declare module Twitter.Typeahead {