Extend a spawn method.

[xgrommx]

Hello @mattpodwysocki. I look on Rx.Observable.spawn and it's awesome that to return Observable. But will be better if exists another method like a wrap the same as in https://github.com/tj/co/blob/master/index.js#L26. I create a small code like so:

Rx.Observable.wrap = function (fn) {
  createObservable.__generatorFunction__ = fn;
  return createObservable;

  function createObservable() {
    return Rx.Observable.spawn.call(this, fn.apply(this, arguments));
  }
};

var spawned = Rx.Observable.wrap(function* (val) {
  var v = yield thunk(val);
  var w = yield Rx.Observable.from([24]).first();
  var x = yield Rx.Observable.just(42).delay(1000);
  var y = yield Rx.Observable.just(56);
  var z = yield Promise.resolve(78);
  return v + w + x + y + z;
})(100);

spawned.subscribe(
  function (x) { console.log('next %s', x); },
  function (e) { console.log('error %s', e); },
  function () { console.log('completed'); }
); // Return -> next 300

[xgrommx]

Also I tried to use like this https://github.com/tj/co#objects but it's doesn't working for Rx.Observable.spawn

[xgrommx]

Closed by #855