possible API for asyncGate.js... what do you think?

ex1.js

function foo(done) {
   setTimeout(done,5000);
}

function bar(done) {
   setTimeout(done,1000);
}

function baz() {
   alert("all done!");
}

// this means: execute `foo` and `bar`, wait for both of them to signal completion, then do `baz`
$AG(foo,bar).then(baz);

ex2.js

function foo(done) {
   setTimeout(done,5000);
}

function bar(done) {
   setTimeout(done,1000);
}

function baz() {
   alert("all done!");
}

var gate = $AG(foo);

// later

gate.and(bar); // you can keep adding to the gate as much as you want...

// later

gate.then(baz); // ...until you start adding listeners

// later

gate.then(function(){ // ...and you can have as many listeners for a gate as you want, 
                      // even if it comes after the gate is already open
   alert("already done awhile ago!");
});