message: refactor(toPromise): simplify type signature and remove unnecessary documentation
diff: import { Observable } from '../Observable';
  -/* tslint:disable:max-line-length */
  -export function toPromise<T>(this: Observable<T>): Promise<T>;
  -export function toPromise<T>(this: Observable<T>, PromiseCtor: typeof Promise): Promise<T>;
  -export function toPromise<T>(this: Observable<T>, PromiseCtor: PromiseConstructorLike): Promise<T>;
  -/* tslint:enable:max-line-length */
  -
  -/**
  - * Converts an Observable sequence to a ES2015 compliant promise.
  - *
  - * @example
  - * // Using normal ES2015
  - * let source = Rx.Observable
  - * .of(42)
  - * .toPromise();
  - *
  - * source.then((value) => console.log('Value: %s', value));
  - * // => Value: 42
  - *
  - * // Rejected Promise
  - * // Using normal ES2015
  - * let source = Rx.Observable
  - * .throw(new Error('woops'))
  - * .toPromise();
  - *
  - * source
  - * .then((value) => console.log('Value: %s', value))
  - * .catch((err) => console.log('Error: %s', err));
  - * // => Error: Error: woops
  - *
  - * // Setting via the config
  - * Rx.config.Promise = RSVP.Promise;
  - *
  - * let source = Rx.Observable
  - * .of(42)
  - * .toPromise();
  - *
  - * source.then((value) => console.log('Value: %s', value));
  - * // => Value: 42
  - *
  - * // Setting via the method
  - * let source = Rx.Observable
  - * .of(42)
  - * .toPromise(RSVP.Promise);
  - *
  - * source.then((value) => console.log('Value: %s', value));
  - * // => Value: 42
  - *
  - * @param {PromiseConstructor} [PromiseCtor] The constructor of the promise. If not provided,
  - * it will look for a constructor first in Rx.config.Promise then fall back to
  - * the native Promise constructor if available.
  - * @return {Promise<T>} An ES2015 compatible promise with the last value from
  - * the observable sequence.
  - * @method toPromise
  - * @owner Observable
  - */
  -export function toPromise<T>(this: Observable<T>, PromiseCtor?: PromiseConstructorLike): Promise<T> {
  - return this.toPromise();
  -}
  +// HACK: this is here for backward compatability
  +// TODO(benlesh): remove this in v6.
  +export const toPromise: typeof Observable.prototype.toPromise = Observable.prototype.toPromise;
  