Promises and ES6

[lekoaf]

Hi!

I tried to rewrite this with Promises and ES6. You should probably check it out and try it before accepting the pull request since the example didn't really work. It does go in to the catch statement atleast with:

{ 
  Error: connect EHOSTUNREACH 93.184.220.20:80
    at Object.exports._errnoException (util.js:1026:11)
    at exports._exceptionWithHostPort (util.js:1049:20)
    at TCPConnectWrap.afterConnect [as oncomplete] (net.js:1081:14)
  code: 'EHOSTUNREACH',
  errno: 'EHOSTUNREACH',
  syscall: 'connect',
  address: '93.184.220.20',
  port: 80 
}

I also bumped the version to 1.0.0 since these are breaking changes.
(Found this repo while looking for soap-clients for a project of mine)

[jtblin]

Thanks for the PR @lekoaf. Out of curiosity, why not just using something like promisify?

I'd be happy to accept the PR with a breaking change as long as the example and tests still work.