anchor.diff:  
   In the example below, all futures are started at the same time by
   +async.par.run+ which returns a +Future[(Int,Int,Int)]+ that completes once all
  -supplied futures complete. After this returned Future completes, the tuple value
  +supplied futures complete. After this returned future completes, the tuple value
   results can be extracted using normal Scala idioms.
   
   .Example 7: +async.par.run+ workflow
  
positive.code: number of workers is limited to two, progress is reported once a second and
  certain failures are retried.
  
  .Example 8: +async.par.run+ workflow with progress reporting and retry
  [source,scala,numbered]
  ----
  for {
  
negative.code: scala>
  ----
  
  .Example 10: +merge+ method fails immediately on the first exception and throws +ConcurrentThrowable+ which can retrieve all exceptions:
  [source,scala,numbered]
  ----
  scala> val t = Vector(longRead("1"),readFail("2"),readFail("3"),read("4")).merge.getTry
  