Status and headers not given to then/success

The [readme](https://github.com/mzabriskie/axios/tree/f2fd9f7dd3a644ddbd25b4bfe59c86313b24a443#response-api) mentions that promises resolve with multiple arguments giving the status code and response headers in addition to data, but most promises library do not handle multiple arguments.

I added a spec [to show it](https://travis-ci.org/mathbruyen/axios/builds/35427410), but I think it requires an API change to work, thus I did not look at solutions yet.

Any advice there?