Add Promise for xray.then()

[kengz]

Add Promise for xray.then()

This solves the feature request for a promise, #62

• Create a new method node.then(cb). Use the node.stream() method, create a promise from the stream, then invoke the then() with the callback cb.
• add test
• update documentation

Checklist

• Code compiles correctly
• Created tests which fail without the change (if possible)
• All tests passing
• Extended the README / documentation, if necessary
• Added myself / the copyright holder to the AUTHORS file

[coveralls]

Coverage decreased (-0.1%) to 95.775% when pulling dd57bb4 on kengz:master into bc5c173 on lapwinglabs:master.

[coveralls]

Coverage decreased (-0.4%) to 95.518% when pulling f444f4e on kengz:master into bc5c173 on lapwinglabs:master.

[coveralls]

Coverage decreased (-0.4%) to 95.518% when pulling f444f4e on kengz:master into bc5c173 on lapwinglabs:master.

[coveralls]

Coverage decreased (-0.4%) to 95.518% when pulling f444f4e on kengz:master into bc5c173 on lapwinglabs:master.

[coveralls]

Coverage decreased (-0.4%) to 95.518% when pulling f444f4e on kengz:master into bc5c173 on lapwinglabs:master.

[coveralls]

Coverage decreased (-0.4%) to 95.518% when pulling f444f4e on kengz:master into bc5c173 on lapwinglabs:master.

[coveralls]

Coverage decreased (-0.4%) to 95.518% when pulling f444f4e on kengz:master into bc5c173 on lapwinglabs:master.

[kengz]

@matthewmueller I noticed there's a X-Ray In the Wild section in the Readme. FYI I used Xray to build this psi-scraper, feel free to include if u feel it's relevant, or it's okay not to as well.

[dougsilkstone]

Can we get this merged?

[kengz]

Is any of the authors available? This is ready to merge

[taisang1996]

I have installed x-ray (2.3.2) by command npm install x-ray, but package do not have this feature.
Try install by command work well npm install https://github.com/matthewmueller/x-ray.

Please update this feature on npm.

[thebarty]

Plus one for mergin this in. Just lost some time on finding this solution. Thanks for the tip!