function combineArray (f, streams) {
  var l = streams.length;
  return l === 0 ? empty()
  : l === 1 ? map$2(f, streams[0])
  : new Stream(combineSources(f, streams))
}
Combine latest events from all input streams
@param {function(...events):*} f function to combine most recent events
@param {[Stream]} streams most recent events
@returns {Stream} stream containing the result of applying f to the most recent
 event of each input stream, whenever a new event arrives on any stream.