function argumentsToArray() {
  var len = arguments.length, args = new Array(len);
  for(var i = 0; i < len; i++) { args[i] = arguments[i]; }
  return args;
}
Merges the specified observable sequences into one observable sequence by using the selector function whenever all of the observable sequences have produced an element at a corresponding index.
@param arguments Observable sources.
@param {Function} resultSelector Function to invoke for each series of elements at corresponding indexes in the sources.
@returns {Observable} An observable sequence containing the result of combining elements of the sources using the specified result selector function.