Act as polyfill

[ForbesLindesay]

We may want to consider using native promises when available in the near future. We would still need to provide Promise.prototype.done and the node.js extensions though.

We would have two options:

1. Extend the built-in Promise constructor when available and export that, export our custom implementation otherwise.
2. Inherit from the built in Promise constructor when available, inherit from /lib/core.js otherwise.

We also have a few options when there is no built in promise constructor:

1. Define Promise globally (in addition to exporting it). Effectively making this library a true polyfill but with some extensions.
2. Define Promise globally, but only add our special extensions to a copy that inherits from the globally defined Promse.
3. Continue as we are at the moment.

[edef1c]

Seems we only extend the global Promise object with Promise#done, and not with nodeify/denodeify.
Other than that, we seem to have this down.

[Zorgatone]

Any update on this?
Would you add the Polyfill just if the Promise global is not defined?
What I'm really interested is the nodeify/denodeify feature

[TehShrike]

@Zorgatone I also wanted to use those functions in other environments, so I published them as then-denodeify and then-nodeify.

[Zorgatone]

Oh ok thank you!