Run Explicitly

Adding run flag to  options to enable adding tasks without kicking off the run.

This allows for adding a series of tasks and running the queues later:
```js
var q = new Queue(['before', 'on', 'after']);
q.add('before', first,  {run: false});
q.add('on',     second, {run: false});
q.add('on',     third,  {run: false});
q.add('on',     fourth, {run: false});
q.add('on',     fifth,  {run: false});
q.add('after',  sixth,  {run: false});

// run the queues
q.run();
```

`run` defaults to true to enable backwards compatibility.

Closes #2