Exposing all Promise method docs

The new methods introduced in YUI 3.15 (https://github.com/yui/yui3/wiki/YUI-3.15.0-Change-History-Rollup#promise-change-history) have had documentation since their introduction, but due to not using `/** … **/` comments they were visible to yuidocs and thus they aren't on http://yuilibrary.com/yui/docs/api/classes/Promise.html.

This PR corrects the comment syntax to bring the method information to that page.

/cc @juandopazo