Support Promises

[dguo]

Hi, is there any interest in adding support for Promises? One technique is to check if a callback is provided, and if not, return a Promise. This method should maintain backwards compatibility.

[yudikubota]

@estliberitas ?

[rzfzr]

Your suggestion worked quite well. This will be merged and published by me with the v9 migration, which is more urgent. I didn't mean to start implementing this till v9 were done, but having this will avoid callback hell during testing all the endpoints.