Sharing data between flow blocks

There are some cases when it is necessary to pass data between the blocks of the flow.

Like there:
http://stackoverflow.com/questions/4234619/how-to-avoid-long-nesting-of-asynchronous-functions-in-node-js
or there:

    function(){
      redisClient.smembers("names" this);
    },function(err, names){
      redisClient.select(0,this);
    },function(){
      redisClient.mget(/* `names` is needed here */, this);
    }    

We have two options:
 1. Keep it in the shared scope - the most obvious and the worst way, since the value could be sensetive and shouldn't be accessed out of the flow.
 2. Assign it to `this.varname` - works well, but looks tricky and can cause unexpected behavior in certain circumstances.
	

So, I've implemented STASH and REVEAL methods for this case:

    this.STASH("names", names)
    ..
    names = this.REVEAL("names")