function httpGetJSON (url) {
	return Observable.create((observer) => {
		needle.get(url, config.httpOptions, (error, response) => {
			if (error) observer.error(error)
			else {
				observer.next(response.body)
				observer.complete()
			}
		})
	})
}
GETs JSON documents from an HTTP endpoint.
@param  {String} url - endpoint to which the GET request should be made
@return {Object} An observable sequence of the fetched JSON document.