#merge-pool#
merge multi requests, process one and response all
npm install git://github.com/neutra/merge-pool.git
var echo = function(input,callback){
var reply = function(){callback(null,input);};
setTimeout(reply, 1000);
};
MergePool = require('merge-pool');
MergePool.run('key',echo,1,console.log);
MergePool.run('key',echo,2,console.log);
MergePool.run('another',echo,3,console.log);
MergePool.run('key',echo,4,console.log);
MergePool.run('another',echo,5,console.log);
// null 1
// null 1
// null 1
// null 3
// null 3